Some TMNT stuff really isn't for little kids.
When Arnold was a wild young kid, he got his first tattoo and formed the Purple Dragons gang. Life was good for Hun until he met a young woman, got married, and settled down. He quit his more outwardly violent gang lifestyle. When his wife got sick, Arnold fell into alcoholism and subsequently became abusive toward his son Casey Jones after the passing of his wife.
He first encountered the Turtles when a then-homeless Raphael found him beating Casey, and drove Arnold off. Arnold's gambling debts also led him to sell some of his son's valuables, and one such incident led to him beating Casey again, this time badly enough that Raphael nearly killed him in retaliation. Splinter intervened before his son could murder Arnold, and decided that Casey would live with them from then on.
Arnold later learned that Casey had been badly injured by Shredder, and swore off alcohol after hearing Angel Bridge disparaging him by Casey's bedside. Later he was contacted by Shredder and a brainwashed Leonardo, who offered him a new life as a minion of the Foot Clan, in charge of the Purple Dragons. Arnold agreed, and was transformed by the mutagen into a more muscular, powerful version of himself. He defeated Angel for command of the Purple Dragons, and used the gang to rob and assault for the Foot Clan.
His new status led to conflict with Casey, who remained loyal to his mutant friends. Arnold decided that he would kill his son if he did not join him in loyalty to the Shredder, and attacked him over the grave of his dead wife, using the Purple Dragons. Fortunately, he was stopped from killing Casey by Angel, who had donned a powerful exo-suit.
During the attack on Burnow Island, Hun was left at the Foot headquarters to guard the facility, and fought Slash when Splinter and the Mutanimals invaded. After the Shredder was seemingly killed on the mission, Hun went missing, drank heavily, and sought out Casey at the Second Time Around store. Believing Shredder was dead, he declared that now he and Casey could be a family again, and became enraged when Casey was disgusted and instead defended the O'Neils from him.
Hun was prevented from attacking them by the arrival of Angel and Alopex, but returned with dozens of Purple Dragons. However, several residents of the street came out to defend their neighbors from the Dragons, and eventually Hun was left on his own. He attempted to sway Casey to his side by arguing that they were the same kind of person, but was arrested by Detective Kara Lewis. However, he was broken free by Old Hob before he could be imprisoned.
Hun came to an agreement with Old Hob, running weapons that the Mutanimals captured in their raids. However, when this arrangement was discovered by Michelangelo, Hun attempted to murder the young Turtle as revenge for alienating him from his son. He nearly killed Michelangelo when Slash intervened, flying into a berserker rage and nearly crushing Hun's head. Hob stopped him, exposing his agreement with Hun.
While working for Hob, Hun also ran a dogfighting ring in Hob's warehouse, which angered Hob and brought him to the attention of Leatherhead.
During the Triceraton invasion, Hun unexpectedly came to Casey's rescue when the young man, now the leader of the Purple Dragons, was attacked by a Triceraton. For a brief time, the two seemed to be reconciling, with Hun seeking a more amicable connection with Casey. However, he retained his violent hatred of all mutants, and tried to divide Casey from his old friends whenever possible. His disgust was reciprocated by Leonardo, who nearly attacked Hun.
When Casey's girlfriend Jennika was accidentally mutated, Hun showed the same loathing for her that he had for all mutants, arguing that mutants had done nothing but make his family miserable. The division between Casey and Jennika was healed after an attack by Karai's ninjas, and an enraged Hun stormed out of the house. Unbeknownst to Hun, Agent Bishop was watching his departure, and showed interest in the man.