In each campaign of Strategic Primer, my strategy game, there have been several extra “players” under the Judge’s (my) control to the game in addition to the human players. I call them “AI” players, and they serve several purposes.
First, they help make up for the lack of active human players. I’d like to have well over ten total players in a campaign, unless it were a campaign with a more directed story (one where the players started off as allies and had to work to defeat a particularly evil enemy, for instance), but I only have three human players so far in the current campaign, which is to say seven including the “AI”s, and only had (not counting the players who initially volunteered but later withdrew or simply didn’t play) eight human players and four AIs in the first campaign.
Second, they help work around the problem of players making decisions based on knowledge of the human being behind the “code name.” Without the AIs, if a player knew all the players (or even knew their backgrounds, or had read records of their previous campaigns), he could make assumptions about another player’s actions that I think don’t fit with the game. Having AIs—particularly if each has a distinct personality and meta-strategy—helps keep the players on their toes.
Third, one of the roles of the Judge is to advise the players, to help them learn the game and improve their skill. But besides my well-known ineptitude at games in general without quite a bit of practice (which applies somewhat less to games like this because I can take as much time as I need), just because I’m designing the game doesn’t mean I know how best to play it. By managing several players himself, the Judge gains insight into how to advise the players. And in my case, I can also gain some extra insight into how to change the game’s design before something becomes apparent to the human players.
Fourth, it helps equalize the effort required by the participants in the game. In most games where a Dungeon or Game Master describes situations and players react, the Judge-equivalent has to do if anything more work than the players to make the game run smoothly, but without AIs (unless there were a dozen or more players with strategies that were complicated or difficult to run) the Judge would have to put in very little effort each turn compared to one of the players. This is because running a strategy isn’t all that much work, at least with reasonable assistive technology (which I admittedly don’t have yet, but still …).
And fifth, if the Judge intends to weave a story into the game, AIs are essential, like non-player characters in a role-playing game. This doesn’t apply in the present campaign, since I don’t intend to impose a story, but would have made them essential in the campaign that I tried to start my junior or senior year of high school.