Can you? Yes.

Should you? No. You personally, as a novice DM, very much no.

This is called a “DMPC”,* and they're very hard to do right. A new DM such as yourself should not have a DMPC. The DM already has the biggest job at the table, and it takes an experienced DM to handle the DM job well while also dividing their attention with a PC of their own.

Aside from being a distraction, a DMPC brings special problems and risks of its own:

• 
  It's very hard to play fair when you have your own PC, because you know things as the DM that a PC can't and shouldn't.


• It's very easy to give your DMPC special treatment and steal the spotlight from the PCs.


• It can make your players try use your DMPC to learn DM-only information.


• 
  When you manage to play fair, the result is not having your own PC after all, just a weaker NPC. So what's the point?

There are ways to avoid these problems, but they take a lot of experience as both a player and a DM. A novice DM is nowhere near able to accomplish that.

For perspective, I've been running games for over 25 years, and I do not feel confident that I could pull off a DMPC successfully, even with all that experience.

If you want to be a player…

DM this game. Then take a break and ask someone else to run the game for a while so that you can be a player. Everyone wins, nobody gets angry at you for ruining the game with your DMPC.

* “DMPC” is the D&D-specific term. The generic term is “GMPC”, since the generic name for “dungeon master” is “game master” (“GM”).

You can have NPCs join the party, but having your own full player character is traditionally discouraged

The rules imply that the DM does not control an adventurer, and this is generally understood by D&D players to be the standard method of play. For example, on DMG p.4:

The DM creates a world for the other players to explore, and also creates and runs adventures that drive the story.

And on page 6 of the same book:

The success of a D&D game hinges on your ability to entertain the other players at the game table. Whereas their role is to create characters (the protagonists of the campaign), breathe life into them, and help steer the campaign through their characters' actions, your role is to keep the players (and yourself) interested and immersed in the world you've created, and to let their characters do awesome things.

The DM will sometimes have an NPC accompany the party, but this most commonly happens on a temporary basis, or as a hireling of one of the PCs. The rules on NPC party members are defined on page 92 of the DMG:

NPCs might join the adventuring party because they want a share of the loot and are willing to accept an equal share of the risk, or they might follow the adventurers because of a bond of loyalty, gratitude, or love.

Technically, even if you did have a full-time "PC" in the party, any character controlled by the Dungeon Master is an NPC, not a PC (D&D 5e Dungeon Master's Guide, p.89):

A nonplayer character is any character controlled by the Dungeon Master. NPCs can be enemies or allies, regular folk or named monsters.

However, new DMs who want a DM-PC are usually just unfamiliar with the concept playing the game without controlling a character. What you need to realise as a DM is that you already get to control multiple characters: every NPC in your campaign. You don't need a party member, and you'll get along fine without one.

There's also a potential conflict of interest when the DM has power and knowledge that a PC will benefit from. Would his PC knowingly walk into a deadly trap or allow the party to walk into an ambush? And what if the DM is tempted to be overly generous when giving his own character items, or to fudge the dice to save his character? For reasons like these, it's usually recommended that the DM not control a party member in the same way as they would if they were a player.

It is generally a bad idea. In your case, it is a particularly bad idea.

I echo what nearly every other answer has stated. Running a DMPC is generally a bad idea. I'll go beyond that, though. In your particular case, it's an especially bad idea.

First, you're a newbie DM. Being DM already requires a great deal in terms of mental resources, to keep track of everything you need to keep track of. Adding a PC onto that is going to make it significantly worse, as it adds even more things to keep track of and think through.

More importantly, though, you want to do this for exactly the wrong reason. Many of the issues that come out of DMPCs come from the DM being too emotionally invested in their character. The only way to avoid them is by, in essence, causing yourself to not emotionally invest in your character - to let that character stay out of the spotlight, to let them make bad decisions even if you know they're bad decisions, to let them fail and lose... things like that. A big part of the enjoyment of being a PC is that you do get to invest in your character. That stuff you want to get by being a PC? If you give that to yourself, you're being a bad DM almost by definition.

It's a bad plan. You shouldn't do it.

Can you? Yes. Should you? Probably not.

There is nothing stopping a DM from having a PC but doing so entails some risks/compromises that you should weigh carefully:

Focusing on your responsibilities as a DM

As a DM, you have a LOT of information to keep track of, both within a given session and from session to session across a campaign. Time spent thinking about and developing your character is time you can not spend developing the campaign for your players. The risk is that their experiences will suffer as a result of your lack of preparation.

Railroading/Metagaming

As the DM, you have an idea of how specific situations that come up might be or should be resolved by the players. Players, without access to your thought process or the information you have access to behind the screen, may not choose the optimal solution, the most fun solution, or even a solution you/the campaign designers thought up.

When you play a character alongside being a DM, there is a big risk that the other players will not experience the same degree of freedom to think and act as they would if you kept to just the DM responsibilities. This is because, unintentionally or not, you are pretty much guaranteed to influence the way the party acts.

The players may get wise to the fact that your character can't help but know one course of action is more likely to produce better results than a different one and exploit this. Even if you keep your character totally silent and only have it tag along, the other players could still exploit the DMPC.

You aren't likely to want to kill your own PC, so they could have the DMPC act in ways that a normal PC, with an interest in self preservation, would not act because they know (or at least think) the DMPC has a level of protection from the DM.

New player development

Given your experience with the game, you no doubt have a certain play style. New players lack this and there is a joy to learning how a player can interact with the game world through their character. When you play a character as a DM, your actions set an example that "this is how things are done" or "this is how I, as the DM, expect things to be done" when, really, there are any number of equally valid play styles.

Jealousy/Frustration

A new player will make sub optimal characters. They'll pick spells they discover aren't nearly as good as they first thought, they'll allocate stats in ways that create frustrating weaknesses, etc.

Then they see a character who probably does not have these shortcomings and think "Gee, I'm playing wrong" or "My character stinks" or, even worse "I'm not nearly as helpful to the group as this other PC." If these sorts of feelings occur because you're playing a DMPC, you can't arbitrate or counsel from a neutral position because you are creating the problem.

A better idea:

DM this group and find a different group to play as a character or switch off DM duties at a later date with one of the players.

Yes, the DM can have a player character

As someone who frequently plays in very small groups (sometimes with only one other player), I often play a character whilst DMing. There are a few pitfalls to be aware of when you make what's known as a GMPC (or more specific to D&D, a DMPC).

Your character should be more in the background

Since you are the DM, you control everything in the world; the locations, the enemies and NPCs, etc. Your other players, on the other hand, only control their character, so they have a lot less agency. Furthermore, since their characters are all they've got, they will want their characters to be front and centre (sharing with each other, of course).

Therefore, if your character starts being in the spotlight too much, then they will feel like they're just watching you star in your own movie whilst they sit back and be little more that a support cast, which won't be very interesting to them.

If you make a DMPC, they should be more of a background character. This isn't to say that they can never have anything related to their backstory come up, it should just happen proportionately a lot less often than things relating to the other PC's backstories. Your character should not be a leader, but a follower. They can still be a fully fleshed out character, but not one who will want to take lead of the others, because...

Your character knowledge and DM knowledge may cross-contaminate

Since you are the DM, you know everything. You know where your traps are, where the best treasure is, and where the plot is going. Ultimately, your players will have to figure these things out on their own without your DMPC giving them "inside information". This means that your character probably isn't going to be doing much problem solving, at best only reflecting what the other PCs have said back at them so that it makes you seem like your contributing to the conversation from a roleplay perspective, but without solving the puzzles for the other players.

Likewise, when it comes to traps, don't check for traps unless one of your players tells you to. I had a rogue DMPC (actually a rogue/monk, but that's not important) and I would only check for traps if another player (since I was the only rogue or rogue-like character in the party) asked my character to, since otherwise, how would I know when it would occur for my character to check for traps when I (as DM) know where they all are? Hence my character was not a leader, was never up front (unless the players had decided that's where he was in our marching order that day) and would never do anything like check for traps unless I was told to.

Your character can die

I'm not sure on your attitude towards character death, so I'm going to assume that you would be not best pleased should your DMPC die (if only because this answer is then more useful for those who would react like that). If you can happily accept character death, then it doesn't matter; they die, move on.

However, if your DMPC does die, there might be a temptation to make their resurrection or whatever more important than it is. Resist that. Their resurrection should only be important if the other players consider it important, much the same as if a simple NPC had died. However, this all depends on how you would react to character death if you were not the DM.

Can you? It depends on the social contract, but generally yes.

Unless your group, as a group, agrees that you cannot then you can. You are the GM and have vast authority over the game world. You can insert as many non-player characters as you like. If you want to have one that is built as though it were a PC and that travels with the party and you consider yours, there is certainly nothing in the rules that would prevent it (though NPCs are often built differently from PCs).

So, the direct answer to your actual question is yes unless the group specifically agrees you should not.

Should you is a separate question, and generally you should not.

However, it comes with a host of issues and is generally discouraged. In particular, it distracts from focusing on the PCs, can easily overshadow the PCs, and makes it hard for you to avoid using "gm-only" knowledge that the rest of the party won't have yet.

There are ways to mitigate those issues, and I have seen GMPCs handled in ways that I consider to be effective. However, those issues require mitigation.

Also, having done it personally (albeit not specifically in a 5e game) I will say it is not as fun as it may sound. You simply don't get the fun of playing while also GMing because you can remove any obstacle from your character's path by declaring that it is so. This removes any sense of challenge. There are other reasons to add a GMPC that might work for some groups at some times (such as filling in a party role that is necessary for that adventure when no one else wants to play it), but it probably won't add a lot of fun for you. It doesn't for me.

The DM can always do anything he wants, but DMPCs are unpopular because they're harder to do well than it sounds. Most games have a degree of antagonism between DM and PCs, in that DM provides challenges and players try to defeat them. But it is awkward to come up with your own challenges and defeat them yourself, which is why DnD is usually not played as a single player game (although you can). Among other issues, it's easy to fall into:

• DMPC stealing the limelight from players


• DMPC making an existing railroading problem worse


• DMPC having plot armor to the annoyance of players

And last but not least, for many years DMPCs have been a staple of gamer humor. As evidenced by this thread, everybody loves to speak out and bond over that one time they had a DMPC that ruined everything and how terrible it was. Because of this, even if you do a good job, your players may not like it simply because of the knee jerk.

No. By definition the DM is not not a player.

Player characters are run by people that are not the DM. The DM has control over situations, aspects, and story that the players do not.

1. The DM describes the environment.


2. The players describe what they want to do.


3. The DM narrates the results of their actions.

There is no uncertainty for the results of a DM run character describing what they want to do. Such a character is part of the environment of the players.

NPC ≠ PC

As a DM, you can run, and probably will have to run, many non-player characters. They are not the same, because the people playing them do not have the same control over the environment that the DM has. In short:

• Having a long running NPC does not make it a player character.


• Applying PC rules to the NPC does not make it a PC.


• The players and the DM have different roles in the game.

Facilitate the Fun

If controlling a long running non-player character helps the DM have fun, then that's a good thing. Be careful to avoid detracting from the agency and fun of the players. Use the characters played by the DM to add to the story and agency of the players.

DM Demesne

Figuring out how to use characters to allow the players to move the story forward and add to the enjoyment of the players is it's own puzzle. That's one of the challenges and rewards of being a DM.

A DM's purpose in the game is to increase the player's fun. As a DM, you won't be solving puzzles, finding hidden loot, playing overpowered characters, and so on. You're crafting a story, and building a set of challenges and puzzles for the player to solve. If you already know the solution to a puzzle, it's not fun to solve it. If you choose to play a character, it should be because the party cannot survive without it (a problem often found when running three-player groups in a four-player campaign module), and not just to have fun.

You'll find that to play a DM player-character fairly (e.g. increasing the players' fun), you'll need to treat your character as a handicapped version of a real player character. No DM exposition (as an NPC might do), no finding traps, treasures, solving encounters, etc. Your player character will need to be as unremarkable as possible while still contributing to combat scenarios. You will not be having any more fun by playing a player-character while being DM, as you'll constantly have to constrain your use of DM knowledge.

As a player, it's really fun and satisfying to beat the DM's challenges. As a DM, it's really fun to challenge the players to do their best so they're having fun. This is why there's two separate roles. It's not that you can't do it (DM fiat is always a thing, the Rule 0 of playing), it's that it is not nearly as much fun as it sounds. You would have a lot more fun as a DM introducing occasional NPCs when the challenges ahead warrant it, rather than having a fully vested player.

Others mention things like player death and so on, and that's partly true, but there's more to it. It means that you have to roll your player-character rolls in the open. You can't fudge numbers any more than the players can. It's more book-keeping, too, although a DM already does a lot, you may find that hosting a whole extra character with inventory and stuff more frustrating than fun.

As others have said, I don't recommend this just because you enjoy "playing", because it's really a lot less enjoyable than being a dedicated player or a dedicated DM. It's an extra level of frustration to get the balance just right. Either you'll steal the spotlight, or be too frustrated that your players can't figure something out but you already know the secret for. I personally don't have a problem with this technique, but I reserve it for situations where the party is not prepared by itself for the challenges that lie ahead.

Advice for a DMPC

You've gotten a lot of advice on how to skip playing a DMPC, and particularly for a new DM, it's good advice and you should take it. If you don't take it, though, and trudge ahead making a DMPC anyway, here's what your DMPC shouldn't do:

• Do not participate in puzzles...


• ...but if you want to give the party a clue, do it through the DMPC. Certainly never solve the puzzle.


• Do not act as the 'face' of the party or generally participate in social situations.


• Do not suggest battle strategy...


• ...but do follow the player's strategy, for good or ill.


• Do not let the party think of you as disposable...


• ...but don't get attached to the DMPC.


• Do not choose an alignment or personality type significantly different from the party's.

They are the stoic monk or the quietly competent right-hand man to the party leader. You're glad they are there, but at the end of the day, they only drive the story when an NPC is needed. They have character and personality, but they never outshine the player(s).