Sylvester Shyster is a crooked lawyer and evil criminal mastermind who generally teams up with Peg Leg Pete. The character has been described by some as a weasel or a rat (the latter being Gottfredson's own interpretation), but his ears suggest that he is rather an anthropomorphic canine.
He first appeared in the comic strip adventure "Mickey Mouse in Death Valley", the first real Mickey Mouse continuity, which was partially written by Walt Disney and drawn by Win Smith and other artists, before being taken over by Floyd Gottfredson (plot and art). In this story, Sylvester Shyster was a crooked lawyer who attempted, with the help of his henchman Pete, to deprive Minnie Mouse of her inheritance.
Shyster and Pete have been causing trouble for Mickey and his friends since then. Shyster is generally depicted as the duo's brain, with Pete acting as the brawn. He is probably the only person Pete will listen to without rebellion.
After Shyster's first appearance, Gottfredson made no further references to his profession as a lawyer, apart from his name. Later creators occasionally referenced Shyster's role as a lawyer, with one story ("Trial and Error," 2007) forcing Shyster to defend Mickey himself in an overseas courtroom.
Shyster disappeared for a time after 1934, but made comebacks in 1942, 1950 and again in various 1960s Italian-created stories. More recently, publisher Egmont Creative A/S (in Denmark) revived Shyster as a regular character, a capacity in which he continues today.