In the Red Dwarf universe, Duane is a bucktooth gimboid, self-described as The Duke of Dork. Duane Dibbley is Cat's alter-ego (also played by Danny John-Jules). While Cat is sleek, sophisticated, graceful and vain, Dibbley wears an anorak and plastic slippers, he's klutzy, and always carries a Thermos. He also has a really bad hair-cut and giant teeth.
You'll see Duane Dibbley in three different episodes of Red Dwarf. The first is in Back to Reality, when the crew of Red Dwarf are killed by the Despair Squid and wake up to find that they've been playing an AR game for the past four years. Dibbley was playing the Cat. The second time is in Emohawk: Polymorph II, when a tribe of gelfs sends an emohawk after the crew. Cat is attacked and the polymorph feasts upon his cool, resulting in Dibbley appearing for the second time. The last time you see Dibbley is in Series VIII, in Back in the Red, Part 2, when Cat decides he, Lister and Kochanski should disguise themselves with mopheads for wigs and dentures in their mouths, posing as the Dibbley family. When questioned what they did on the ship, they replied, "Computer programmers."