Captain 6 was a really weak guy like The Scratch Cat. He bragged about being the strongest and most evil Number Captain, but he's just some edgy weakling in a shoddy vampire costume. He was so weak, that The Scratch Cat and The Stupid One have both managed to defeat him.
He was created as a fusion between Captain 1, Zalgo, and The Scratch Cat. He got his captain-ness from Captain 1, his edginess from Zalgo, and his loser-ness from the Scratch Cat.
He was killed when he tried to take on Weegee in a fight. Weegee used his Instant Death StareTM, which had predictable results.
Some people keep trying to revive him, but he instantly dies again every time you try to revive him.