Arzt is one of the "Lost" producers' greatest ghoulish jokes. Brought in late in Season 1 to address pretty much every complaint fans and critics had about the series up until that point, it sure seemed like Arzt was going to become an even more annoying Hurley (particularly when the producers started saying he'd return in Season 2). And then he was taken out of the picture in one fell swoop (and one great, sick joke). He returned in Season 6 to help Ben Linus plot his overthrow of the sideways universe school where both worked.
Finest hour: See, we've been warned the dynamite is unstable. But we've mostly forgotten that when Arzt, in a fit of passion, sets the pack down a little too hard and is blowed up real good. "Dude, you've got some Arzt on you."