Tim

Tim is a Caster skeleton found in the Cavern. He can be recognized by his Wizard Hat. Just like any other caster, he will randomly teleport himself to a visible part of the screen after shooting three Chaos Balls. Defeating Tim is the only way to obtain the Wizard Hat and the There Are Some Who Call Him... achievement.

Tim is immune to the Poisoned debuff.

Trivia

 * His name is a reference to Tim the Enchanter from Monty Python and the Holy Grail, as confirmed by Blue on the Terraria IRC.
 * He is wearing a Robe, which is an item that can be crafted and equipped by the player.
 * Dark Casters also wear this robe. In fact, they look identical, except for Tim's Wizard Hat
 * A way to spawn Tim would be to go on a server, place a Bed in the Cavern zone and set your spawn there. Log out of the server and log back in. Tim will have most likely spawned. (Requires more testing.)

History
Tim Tim Tim Тим Tim