Tim

Tim is a Caster skeleton found in the Cavern. Appearing similar to Dark Casters, he can be recognized by his Wizard Hat, which is guaranteed to drop when he is defeated. Like any other caster, Tim will shoot three Chaos Balls that pass through solid blocks before teleporting to another visible location on screen. Tim is immune to the Poisoned debuff.

In the PC version, wearing one of the gemmed variations of Robes will increase Tim's spawn rate from 1/200 to 1/50.

Encountering and killing Tim grants the Achievement There are Some Who Call Him....

Trivia

 * Tim's spawn rate increase is described in changelogs as occurring if the player "need[s] his hat". This bonus is actually triggered by wearing one of the gem-crafted variations of robes- all of which can serve as half of a two-piece armor set with the Wizard Hat that Tim drops, granting the player a 10% increase in magic critical strike chance.
 * Tim's name is a reference to Tim the Enchanter from Monty Python and the Holy Grail, as confirmed by Blue on the Terraria IRC.

History
Tim Tim Tim Тим Tim