Sebastian Longquin is a minor character in The Amazing World of Gumball. He is an imaginary ex-boyfriend of Penny's that Darwin made up in The Date. He is apparently rich, successful and has done well with his life as a whole.
Despite only being shown on a strip of cardboard, Sebastian appears to look somewhat like an anthropomorphic lamb of some sort. He is well-dressed, and his hair appears to be styled nicely. His bad dental hygiene may suggest that he is from Britain, since this is a stereotype associated with that particular region.