Valve's boss and the Lord of All PC, or something, Gabe Newell is a large boss character in multiplayer dungeon-'em-up Crawl.
A hypnotic gif of Gaben was posted over on developer Powerhoof's site. Seriously, I can't stop watching it.
The best bit is, of course, the fact that when he powers up he grows a beard and pulls his knives out. Oh, Gaben.
It's not an April Fool's day thing, as developer Barney Cumming pointed out in the comments section, and he's aiming for the new boss to be introduced in the next update - though there's no timeframe on when that will hit right now.
We had a look at Crawl when it was in an even earlier state some months ago, but even then it was great fun.