Dr Frankenollie is an anthropomorphic primate and mad doctor.
In 1995, this manic mad scientist owned an enormous castle in downtown Mouseton. In the basement there, he had been constructing an enormous monster known as Julius, as well as a brain-switching machine, and he put out an advertisement in the newspaper offering a job. The ad was answered by Mickey Mouse, who did not realize that the "job" was, in fact, to have his brain switched with that of Julius. Frankenollie successfully completed the experiment, however, the resulting surge of electricity seemingly killed the doctor, turning him to a pile of dust and bones. After a series of mishaps, Mickey switched his brain back, and made Julius tow him and Minnie Mouse to Hawaii.
Although Frankenollie was by all appearances dead after the brain-switcher reduced him to dust, he seemed to have had some safeguards in place, as he soon returned to plague Mouseton. After this apparent resurrection, the doctor began creating an fleet of robotic reconstructions of famous heroes and villains, dubbed Tronics, and having them fight each other, presumably for his own amusement.
Eventually Frankenollie decided to enact his revenge on Mickey Mouse for ruining his plans and freeing his monster, by attempting to infect his computer using various computer viruses of his own invention. What he attempted to gain through this trickery (beyond ruining Mickey's computer) is unknown.
Also unknown are Frankenollie's whereabouts currently, as he has not been seen since the early 21st century.
Behind the scenes
Dr. Frankenollie first appeared in Runaway Brain in 1995. Although this was his only film appearance, Frankenollie remained moderately popular through the late 20th and early 21st centuries, even having a figure in the Walt Disney Classics Collection (a series of collectible sculpted figures) and a Tsum-Tsum version of himself in the popular Tsum-Tsum series of toys.
Interestingly, Frankenollie's role was originally meant to be given to Professor Ecks, however, this was vetoed by Disney higher-ups, possibly due to the fact that Frankenollie is reduced to ash in the film, a fate that Disney might not have wanted to befall one of its oldest villains.
Frankenollie has appeared in Disney comics; however, it was not in a new story, but rather a comic remake of Runaway Brain.