Thief

thief, n., D&Dism 1. in general usage, one that steals, esp. stealthily or secretly; one who commits theft or larceny; Middle English theef, from Old English theof; akin to Old High German diob "thief"; predates 12th c. 2. in D&D, a character class, emphasizing stealth, dodge and trap detection abilities over combat abilities. 3. in fantasy milieu, the profession of an individual who, sometimes in concert with a "guild" of thieves, seeks fortune through theft, espionage, assassination, chicanery, and cleverness. See assassin. Also rogue, rake, skofflaw, roustabout, burglar, hijacker, robber, pickpocket, highwayman. [GJ1]
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Addendum: The original D&D "thief" class was inspired by Bilbo Baggins from The Hobbit; indeed, the creators of D&D pretty much assumed any halfling character would be a thief. The archetype of the thief in modern fantasy literature is based more closely upon the Gray Mouser from the novels of Fritz Leiber. [GJ1]