Games : Who is the big bad jellyfish?

This is something that's been bothering me since the first time I played Portal. Who is the big bad jellyfish, and what are they wanted for? This drawing appears on a wall in an office right before the first time you meet a missile launcher. This one:

And the lead up to the office, if you want to find it for yourself:

So, is there an explanation for this? Given Valve's penchant for background storytelling through graffiti/environment, I doubt it's just an Easter Egg that some developer sneaked into the game.