Nuffle is two things. First and foremost, he is the God of BloodBowl as described in the fluff (background) for the game. [This needs expansion, if you read this, feel free.]

He may also be found on many FUMBBL IRC channels, however. There, he is a bot - a program connected to the server with a certain functionality - and not an actual person.

Nuffle is, in effect, the channel services application. It hands out the correct permissions, keeps channel topics set, and more such maintenance tasks.

You can apply to have Nuffle join your own chat channel if you wish. This is done by submitting a support ticket.