Mr. Fixx was Derek Powers' personal assistant and henchman. He was a ruthless brute, devoid of any sense of morality or mercy. Although he is the secondary antagonist, Mr. Fixx turned out to be more dangerous than Derek Powers (at least before Powers' mutation), as he held against Terry (who was in the Batman Beyond suit) and almost killed him.
Little is known about Fixx's past. He was not very talkative, but he was very threatening nonetheless. The scar under his blind left eye indicated that he had previous physical confrontations.
Fixx was trusted with various tasks, including the most illicit errands. He could serve both as his chauffeur and as Power's brawn. He personally murdered Warren McGinnis, and made it look like an unprovoked attack by a gang of Jokerz. He also assured Powers that he wouldn't hesitate in killing young Terry McGinnis, should he interfere.
Fixx was also in charge of supervising the shipment of the nerve gas canisters to Vilmos Egans. When the new Batman showed up, Fixx took off with the cargo. Batman broke into the hovercraft, and Fixx had activated the auto pilot, and engaged him with electrified brass knuckles. Fixx even complimented Batman's strength, but mocked his intent to carry the legendary hero's mantle. At this point Terry assured him he was the real deal, and slugged him hard, causing Fixx to collide with the craft's controls. The ship spun out of control and crashed in Gotham's bay, seemingly drowning Fixx together with the nerve gas vials.