Ben was forced to work with Reinrassic while trapped on Turrawuste in Alone Together. During a fight with him back on Earth, Kevin damaged the teleporter Reinrassic attempted to use to escape, sending Ben and himself to Turrawuste which is used only as a routing station. Though they needed each other to survive, saving each other on multiple occasions, Reinrassic showed the typical Highbreed hatred of other species, forcing Ben to walk ten paces behind him and insulting him constantly. Reinrassic eventually lost his hand saving Ben from a Rodilia Dentia, resulting in Swampfire reattaching it. Eventually they made it to the teleporter but Reinrassic placed himself in exile in Turrawuste, believing himself infected by Ben.
In War of the Worlds: Part 2, after Ben healed the genetic damage in all Highbreed by fusing them with alien DNA. Reinrassic was unaffected by this because of his healing from Swampfire, as the vine used to reattach his arm has now spread up to his elbow and changed his DNA as well. He, despite his original self-imposed exile, realized that the Highbreed's views on other species were wrong and that being fused with another alien's DNA wasn't a curse, but rather allowed the Highbreed to survive. This caused the Highbreed Council to elect him as the new Highbreed Supreme, the leader of all Highbreed. He called off the invasion and shook Ben's hand as a show of respect.In If All Else Fails, Reinrassic aided Ben to stop a Highbreed Failsafe weapon left over from the war, which had been activated by Highbreed Officer who was unaware the war was over. He told the officer he is the Highbreed Supreme but the officer noticed his arm and didn't believe him. Reinrassic opened his palm to reveal the Imperial Seal, and the officer knelt before him, apologizing. He ordered the officer to shut the weapon down, but the officer revealed once it was activated it cannot be stopped. However, Ben and Gwen came up with a plan to enter the weapon and deactivate it from the inside. They managed to stop it. The Highbreed Officer took control of it, preventing it from destroying a Nuclear power plant. Reinrassic congratulated Ben for stopping the weapon, but Ben revealed the Highbreed Officer's sacrifice. However, Reinrassic told Ben that the Highbreed who died was a soldier doing his duty and that there was no greater honor for a Highbreed. Gwen asked if there are any more Highbreed weapons on Earth. Though he said there were none, he mentioned that he will check the records anyway. Ben then offered him a ride home.
Ben 10: Alien Force
Reinrassic III's name is based on "Reinrassig," which is a German adjective meaning "purebred". This is ironic because Reinrassic III is the one who convinces the Highbreed to give up their purity.
- Reinrassic III was the first Highbreed to be mutated.
- Due to not being accustomed to human introductions, when Ben introduces himself as "Ben, Ben Tennyson," from then on, Reinrassic refers to him as "Ben Ben Tennyson," a reference to Arthur Dent's introduction to Slartibartfast in The Hitchhiker's Guide to the Galaxy as "Dentarthur Dent".
- Reinrassic III is the only Highbreed to have its additional DNA identified.