A corrupt Enforcer sergeant who was secretly leaking information to Katscratch. Thompson used to abuse Chance and Jake back then during their old Enforcer days back then. Thompson also has violent methods in dealing with criminals such as trashing Pop Perkins' stand when he accused him of trafficking counterfeit bills. The reason that Thompson hurt Pops was because he was angry at Chance. It was also revealed that Thompson and Chance grew up in the same neighborhood together as five year olds. Thompson was abused by his alcoholic parents and would often take it on Chance, who lived in the orphanage. One evening, Thompson gave Chance a horrible beating and left him in the alleyway when the rain started. Fortunately, Chance was found and adopted by Pop Perkins, a kind comic book salesman who just lost his son and wife. Thompson learned about this and grew to hate Chance for having what he never got to have. Arnold was one of the twins chosen randomly and stolen at birth by Dr. Robinson who reported him as a stillborn to Harry and Charlene Thompson. Arnold is actually Chance's long lost brother who was raised and abused by Harry who was an alcoholic and while Charlene would just steal objects for money. One evening when Arnold became a college student, Harry was discovered to have been a serial killer who murdered homeless people and murdered Charlene for reporting him to the Enforcers. Before Charlene died and after Harry was arrested, she told Arnold how he was adopted. Arnold went to question Dr. Robinson and eventually killed him in anger once he learned the truth. Arnold stalked Chance and grew to hate him for having the life that he could have had if it hadn't been for Robinson. Arnold began an intense physical workout program to reduce the anger he had. Although Arnold's body had been honed to near-perfection and attracted many women, his violent obsession for Chance increased. Arnold's boss Dark Kat eventually had him turned into a cyborg so Arnold can confront his own brother about his existance and kill him.
-He's just like the Flash villains Cobalt Blue and Zoom. Like Cobalt Blue, he is the twin brother to the hero and very jealous of his own brother's success and had a troubled childhood. Like Zoom, Arnold had a troubled relationship with his parents who barely spoke to one another and his father is a serial killer.
-He's like Venom from Spider-Man as well since he has a violent hatred towards the hero and willing to kill the hero's loved ones to achieve nothing more but vengeance.
-He's also like Detective Arnold John Flass and Swat Lieutenant Brandon from Batman: Year One since he is an athletic and corrupt cop like Flass as well as having a violent approach to law enforcement like Brandon.
-Like the character Barry Dylan from Archer, he resembles T-Bone and was converted into a cyborg.