The Tick became the Tick when . . . wait, how? The Tick's origin is mysterious. He simply appeared and went to work. He has a childlike mind and operates in an undetermined environment known simply as The City. Why?
That's because he is a child. That child was bitten by a tick and is slowly dying of Lyme disease. He's imagining that he's developing superpowers bestowed on him by the tick that bit him.
This is 1 of 10 dark and wacky fan theories that explain children's TV shows. Screen Rant describes them all, including the origin of SpongeBob SquarePants, who Inspector Gadget really is, and the unreality of Ash Ketchum's experiences in Pokémon.
-via Geek Tyrant