Once I saw this picture, I had to make that face.

The Dopefish: the 2nd dumbest creature in the known universe and has appeared in nearly every id Software game since, and even in some games that they have connections to like 3D Realms with Rise of the Triad and Remedy with Max Payne. An easter egg of easter eggs

Swim Swim Hungry.

Ah, the Dope Fish... good times. I love all its cameos in modern games, like the one that was spray painted on a wall in Deux Ex: Human Revolution. That totally took me by surprise when I saw it in game. xD

So that's where that's from. I now understand Elmo's avatar.