Doctor Nefarious was a robotic mad scientist who hated organic life forms, despite formerly being one himself. He was the archenemy of so-called "superhero" Captain Qwark, and later the most recurring nemesis of the courageous duo, Ratchet and Clank. Nefarious was the main antagonist of Ratchet & Clank: Up Your Arsenal, plotting to turn all organisms into robots, much like what happened to himself. He was eventually defeated, but survived. He made a number of cameos in further games, and finally returned as the main antagonist in Ratchet & Clank Future: A Crack in Time. He planned to gain control of time itself and remake history. He was again defeated, retreating into hiding after being rescued by his servant, Lawrence. He was then searched for all throughout the Polaris Galaxy by Galactic President Qwark (who took a great deal of credit for his defeat despite not being of much help the Ratchet and Clank), mentioned numerous times in the comic miniseries. He is set to reappear in Ratchet & Clank: All 4 One as a playable character along with Ratchet, Clank and Qwark.
Doctor Nefarious was characterized as being extremely evil, eccentric, maniacal and insane. He had absolutely no remorse in his actions and cared only for his personal gain. He showed enjoyment in his diabolical endeavors. His treatment of the Fongoids also showed much cruelty, and his disregard for Courtney Gears' affections showed him to be very cold and uncaring, despite Qwark's insulting her offending him later, suggesting he retained at least some feelings for her but chose not to show them. He showed complete impatience for his servants failing him, shown when he threw a complete fit of rage at Lord Vorselon and entirely double-crossed the Valkyries possibly due to Cassiopeia's disobedience. The Doctor was also well-known for being conceited and egomaniacal; his inventions and structures were usually made in his image, his robot servants commonly resembled his features and/or had mannerisms like his, and he tended to pass his ideals onto his subordinates.
Despite the Doctor's extreme hatred for organic life. He was not above working with them to obtain his desires. Nefarious has also shown to be extremely cunning, knowing full well how to manipulate others to get what he wants. This is shown by how he forged an alliance with the Tyhrranoids, the Fongoids, and the Zoni; as well as how he had Lord Vorselon and the Valkyries come to his side with the respective promises of a new body and a home planet. However, that did not stop him from betraying them when either their usefulness had run its course or they disappointed him.
After being turned into a robot, Dr. Nefarious acquired a vast array of powers and abilities that greatly contributed to his fighting skills. His hands were made into sharp metal claws for close-quarters combat. He could also fly with booster jets in his feet. A pair of retractable wings extended from his back and were used to keep balance when flying, also allowing him to hover low above the ground. The doctor also wielded blasters on occasion, such as duel ones that fired red-purple laser beams. Mainly, Nefarious controlled and fired various forms of energy from his hands, utilizing many different kinds of attacks against his enemies as demonstrated numerous times in his battles with Ratchet and Captain Qwark.
Dr. Nefarious could rain down rainbow-like streams to hit targeted areas, raise walls of energy from the ground, and move a floating circular vortex. He could also project holograms of himself that would charge and slash with a claw and lob purple energy balls that created shockwaves when hitting the ground. While flying, he could project a blue dome shield, fire continuous purple or orange energy beams, conjure a barrage of missiles that would target all over the ground, and send rod-shaped streams of his energy across the ground. Some attacks exhausted the doctor and took much power; after some attacks, he would stumble backwards and hold his head briefly before standing himself upright, and when initiating others, he let out a loud shout.
Dr. Nefarious would also occasionally summon his robotic minions to aid him in battle, having them teleport onto the battlefield, or simply order assisstance from Lawrence, who used the doctor's separate weapons to help him. It was not often that Nefarious battled his aversaries himself, often having his servants do his work for him unless all options were exhausted or he had a personal desire to fight.