Duff Man is the muscled official mascot of Duff Beer in the Simpsons. He has appeared in three episodes so far, and only talks about himself in the third person. Duff Man's real name is Phil, and enjoys parties, drinking and girls. His random catchphrase seems to be "Oh Yeah!" Duff Man wears a cape (that says Duff on it), a hat (that says Duff on it) and a Batman-esque utility belt (which holds cans of Duff Beer). As Moe's Tavern regular Lenny puts it, "A guy in a costume that creates awareness of Duff".
Duff Man appears to bear an uncanny similarity to Zapp Branigan from Futurama, with inane lines and freakishly blonde hair. However, his luck with women is significantly better:
Titanya (Bargirl with two large...well, work it out): Eww, I thought you said if I slept with you I wouldn't have to touch the drunk!
Duff Man: Duff Man says a lot of things, Oh Yeah!
Unfortunately, it is not clear at the moment whether or not Duff Man is in fact alive, as he was harshly attacked by Moe the bartender for sticking a sticker over his ugly mug...
Duff Man :*Watering grass* That brown patch needs a little H2O, Oh Yeah!
Moe: *Places a large promotional sticker over Duff Man's mouth* Hey Duff Man! How do you like it if I put a sticker on your face?
Duff Man: *Rolling around on ground* Duff Man, can't breathe! Oh No!