The "nom de crime" (?) of James Bolivar DiGriz, better known as Slippery Jimmy DiGriz. He used to be a very successful intergalactic criminal of varying sorts, until he was caught by The Special Corps, and convinced to work for them (set a thief to catch a thief, etc). He has various skills including disguise, weapons, electronics, and a very quick brain (definitely not a moron, as one above writeup used to say)

He's the main character from a series of books by Harry Harrison, starting with the not-terribly-imaginatively named The Stainless Steel Rat, and continued with The Stainless Steel Rat's Revenge, and The Stainless Steel Rat goes to Hell. There may be others, but I haven't seen them.