Theo raeken
Theodore Raeken, better known as Theo Raeken, is a supporting character on Teen Wolf who made his first appearance in Season 5. He was the first Chimera created by the Dread Doctors who managed to successfully complete his transformation without rejection, though he was not considered a true success. He went to school with Scott McCall and Stiles Stilinski up until the fourth grade, which was when his family left Beacon Hills, a year or two after the death of Theo's sister, Tara.
Theo returned to Beacon Hills for his senior year in the autumn of 2012 and wasted no time seeking out the McCall Pack in hopes of joining them. He posed as a recently-bitten Werewolf whose Alpha died before his first full moon, leaving him as an Omega; in reality, Theo was trying to get close to the members of the pack, as he planned turning them against their Alpha Scott McCall and eventually killing him in order to steal his powers and become Alpha himself, coveting the unique combination of supernatural creatures that made up the pack.
Unfortunately, Theo's plan, while perfectly executed for the majority of the half-season, was foiled when Mason Hewitt arrived and stopped Liam Dunbar from killing Scott at the last moment (since Theo, knowing only a Beta of a True Alpha's own making could steal their power, needed Liam to become an Alpha first in order to steal the power for himself). As a consolation prize, Theo used the Dread Doctors' green serum in order to resurrect four of the previously-killed "failed" Chimeras whose bodies were left at the Nemeton, creating his own Chimera Pack in which he was the self-appointed "Alpha" (despite the fact that he was neither a real Alpha nor a real Werewolf).
Throughout Season 5, Theo continued his quest for more power After Theo's release, he maintained his usual survivalist personality, but slowly began to change as a result of the McCall Pack's influence, especially once Liam had destroyed Kira's katana so he couldn't be sent back to his underground prison. By the end of the first half of the sixth season, Theo demonstrated genuine concern for people other than himself when he helped prevent Liam from being captured by the Ghost Riders and fought alongside Scott, Malia Tate, and Peter Hale (a former "bad guy" who was also on a redemption arc of his own) against Garrett Douglas and the Ghost Riders as well. with the help of his packmates, only this time, he focused his sights on stealing the powers and lycanthropy of the Beast of Gevaudan, who had recently been resurrected by the Dread Doctors. To do this, he pursued several different leads that he thought could help him achieve his goal, including obtaining Belasko's talons, capturing Deucalion (the only surviving expert in stealing powers from other creatures), and attempting to capture Lydia Martin, knowing that her Banshee connection with Jordan Parrish, the Hellhound prophesied to battle the Beast, would lure both Parrish and the Beast to him. He even killed two of his "Betas," Tracy Stewart and Josh Diaz, in order to steal their powers of Kanima venom production and electromagnetokinesis, respectively.
However, Theo's plans once again failed when the Beast proved immune to his venom. When he tried to retaliate against the McCall Pack for thwarting his plans (due in part to Deucalion, who was secretly working with Scott and had allowed himself to be captured) Kira Yukimura, with the help of the Skinwalkers, summoned Theo's deceased sister to drag Theo through a sinkhole and trap him underground. Theo's remained imprisoned beneath the underground tunnels of Beacon Hills until he was set free by Liam and Hayden in Season 6's Ghosted.