Darwin WAS a very happy and positive person. He was optimistic, always trying to see the best in most of the scenarios he is in, and was always used as a doormat. but after his brother Gumball encouraged him to speak his mind, he became rude, mean, and would hurt people's feelings. He has no filter whatsoever, and his words can be harsh. Basically his brother set off a monster. Darwin is an orange goldfish with arms and legs, and is adopted.