Mortimer's name was originally meant for Mickey Mouse but Walt Disney's wife Lillian thought the name made Mickey seem pompous. Years later, the name would be used for a new character created to be a rival for Mickey. Mortimer only appeared in the cartoon "Mickey's Rival" and was never seen again until 2000 when Mortimer's popularity skyrocketed and landed him roles in several Mickey Mouse related material.
The first was created by Floyd Gottfredson for Disney studio. He was Minnie Mouse's ranch-owning cattleman uncle. He first appeared in the comic strip Mickey Mouse in Death Valley (1930). After that, he appeared in many Mickey Mouse comic strip adventures in the early 1930s.
In Mickey Mouse Works series, Mortimer is once again the main antagonist along with Pete. Here, Mortimer is Mickey's neighbor and is still competing with Mickey to win Minnie Mouse's heart. In the television series House of Mouse, Mortimer gets a role as a recurring character. Mortimer appears many times as a guest and tries to trick Mickey or Minnie into breaking up.
Mortimer's most recent appearance is in the CG animated series Mickey Mouse Clubhouse. He has a non-speaking role in Minnie's Birthday seen sitting beneath a tree, playing a guitar. In this appearance, Mortimer wears the orange shirt from Mouse Works with yellow polka dots, blue pants and yellow shoes.
Related: http://spanengrish.blogspot.com/2012/03/horace-horsecollar.html | http://spanengrish.blogspot.com/2006/11/what-happened-to-clarabelle-cow.html | http://spanengrish.blogspot.com/2006/12/what-if-it-was-oswald-lucky-rabbit-club.html