Mr Slicker is an anthropomorphic mouse.
Charming, polite, dapper - all words that seem to describe the millionaire Mr. Slicker, though, once his true colors are revealed, it becomes clear that these are not entirely accurate descriptors. Slicker can indeed perfectly play the part of a gentleman, but he's also a manipulative scoundrel willing to use even illegal avenues to gain what he wants.
In 1930, he hired Butch, Snake, and another fellow, all robbers, to steal eggs from Marcus Mouse. Slicker was romantically interested in Marcus's daughter, Minnie, but she was already dating Mickey Mouse. The theft of eggs orchestrated by him put Marcus in financial straits, and he leveraged the situation to his advantage, offering to pull the old farmer out of debt under the condition that he and Minnie be made and man and wife. As the situation worsened and the blame for it managed to be placed on Mickey, Slicker got his way; he and Minnie became engaged to each other and planned their wedding, though Minnie did not truly love him and only agreed to marry him to help her father.
Though he may have sensed victory at first, Slicker's plan did not pan out. Mickey had rallied Slicker's gang of robbers to his side by revealing that Slicker was trying to cheat them, and they revealed to the police that Slicker was a thief before he could wed Minnie. Slicker and his gang were arrested.
Behind the scenes
Mr Slicker first appeared in the comic which bears his name, Mr Slicker and the Egg Robbers. The story was originally released in serialized form across newspaper strips. The strip in which he debuted was released on October the 8th, 1930. He was the main antagonist of the strip.
He provided the inspiration for the later character Mortimer Mouse.