Jervis Tetch has what you might call an unhealthy obsession with all forms of headgear. From derbies to turbans to helmets, he'll steal them all. But the thing he desires most is Batman's cowl.
Recently, he became tired of stealing hats and began using hats to commit other crimes. Last time he escaped from prison was during a prison softball game, when he stole home plate along with Warden Crichton's cap, and just kept on going. It is unknown whether his obsession will resurface, however.