Doug Shablowski

Descriptionn
Doug "The Doppelganger" Shablowski, is an otter that made his first (and probably only) appearance in the episode Temp Check as the main antagonist. He is an otter that just came to the City. He began working as a temp (temporary worker) for Rigby, but then started to copy Rigby's actions, appearance, and voice. Later in the episode, he actually becomes Rigby, and was very hard to tell apart from the actual Rigby. In the climax of the episode, Doug was briefly chosen over Rigby as the "real" Rigby; but since the real Rigby would never give man hugs like Doug did, he is soon found out by Mordecai and gets arrested. Additionally, he apparently had been pulling this scam across the country and was a wanted criminal.

Appearance
Doug is a brown otter with black, long whiskers and a round, black nose. When he first arrived at the park, he was wearing a white, long-sleeved shirt, blue jeans with a belt, and an red and white trucker hat. To copy Rigby, he stopped wearing almost all his clothes (except for his hat).

Abilities
Doug, as his nickname implies, is able to copy a person's voice, appearance, personality, and general abilities. He began taking Rigby's form when Mordecai and him were trying to make an impression of him. He would later copy Rigby's hairstyle, gain the black circles around his eyes and point his tail the way Rigby does. Doug then finished his transformation by becoming an exact copy of Rigby.

Doug also seems to be able to take the person's memories, or at least learn them incredibly fast. During a trivia test, he was able to correctly answer questions about Rigby.

Trivia

 * The name "Doug" is an anglicized form of the Scots-Irish word 'dubh' meaning "dark."
 * Doug seems to have no shame considering the fact that he willingly took off all his clothing to emulate Rigby.