Little has been revealed of Dementor's past or origin. He was apparently well-known as a supervillain before Drakken became a high-profile evil-doer; a running gag from the earlier seasons has others confuse Drakken for Dementor, much to the former's chagrin.
He was voiced by Patton Oswalt who also plays him for the 2019 live action film of the same name.
Dementor is a better scientist than Drakken, and he is also capable of stealing devices for his own needs. His henchmen are of superior quality, as well. Kim generally has to work hard to foil Dementor.
In Dementor's first major appearance, he was established as Drakken's nemesis, mostly because he does a better job at being a villain than Drakken. He made a weapon that could warp reality within a large radius. Drakken tried to steal it and unintentionally activated it, but Kim managed to stop it from detonating and defeated Drakken and Dementor. Later in the series, Drakken posed as Wade to trick Kim and Ron to steal from him.
His next major appearence, he steals a coffee machine from a high tech lab, but Kim and Ron try to stop him. Using his new weapon, the "Bondo Ball", he manages to escape while Kim and Ron end up being attached to the people they dislike the most. To find a cure, Kim and Bonnie go to his hideout, but get captured. It is then revealed that Professor Dementor plans to use his Counter-Electrodynamic Concentrator to steal electricity from the world and force everyone to pay him in order to use it. Things Seemed hopless, but Ron managed to break into his hideout and fused him to his mutant guard dogs.
After the movie "So the Drama", Dementor tried to commit another robbery, Kim easily bests Dementor with her new battle suit, but escapes by putting Ron in peril. Seeing the power it posses, he plans to use if for himself. He later manages to trick Kim and Ron to come in a trap he set to get data on the suit (so he could control it later) and the three of them escape. He returns to control the suit which Ron was wearing to be good at football and the two battle. Ron wins the fight and Dementor wears the suit, but was beaten by Rufus, who was using his controls to stop him.
His final major role took place near the end of the series. He sent his henchmen (including his brother in law Myron) to kidnap Kim and force her to reveal the battle suits location. This mission failed and her cousin Larry was caught instead. The two team up to steal the suit, but by the end of the episode, it turns out that Larry tricked Dementor so he could have a great Birthday. Larry used the suit and defeated Dementor for the last time
- His real surname may be "Demenz" (the German word for dementia), but as that was learned in a Dream (Rewriting History), it is unclear how reliable that information is.