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.

Note, seeing that this does say a lot about the lore of Portal, spoliers are ahead.

Acording to the Half-Life Wikia, the Big Bad Jellyfish is:

The Big Bad Jellyfish is an Easter egg found in this level. It is in a side room on the corridor just before you find the first Rocket Sentry seen in the game. It is a pencil drawing on the wall of an angry looking jellyfish with the text "THE BIG BAD Jellyfish WANTED" under it. Both Jellyfish may have been drawn by Doug Rattmann but there has been no confirmation of this.

The second jellyfish it mentions is probably the Nice Little Jellyfish, found in another room.

Doug Rattmann, or the Ratman, is a former employee of Aperture. In the story, he is the reason that Chell tested first, as he thought she could make a difference.

My own theory is that it was drawn by a child during "Bring your Daughter to Work" day, which was the day GLaDOS was activated, and killed a lot of people. A scared child (even possible young Chell) could have drawn that after seeing GLaDOS activating (hinting to Studoku's comment).

For what the jellyfish(es) truly mean, or who truly created them, no one knows. We only have our rumors and theories, as Valve has not spilled the beans (yet).