Jack Jeebs is an alien living on Earth in the disguise of a pawn shop owner who deals in stolen objects, both alien and human. Jeebs has always been a shady character but has proved useful for Agents Kay and Jay. He has watches and other such stuff for humans, but he also has highly illegal alien technology and guns for the aliens. Jeebs is played by Tony Shalhoub in the films and for a few episodes of the animated series, and is voiced by Billy West in the remainder of the animated series.
Jeebs is an unknown species of alien. His head can be shot off, and it regrows immediately, but never looks exactly the same and stings immensely while regrowing. This has caused Jeebs getting his head shot off to become a running gag in the films and show (mostly when he either angers Jay or Kay, or he refuses to tell them when they need information that he has). It appears that it will grow back no matter what, and it can regrow an infinite amount of times.