Tarakis was an alien shape-shifter who infiltrated the Asgardians,appearing to be one of them. He was actually an agent of Thanos. He was adept at making potions and was soon trusted with the care of Odin, still recovering after captivity and torture by the Dark Gods. He tried for sometime to act as Odin's advisor but was dismissed, mostly because the "Odin" he approached was actually Loki in disguise. When the real Odin returned, Tarakis was still there to help in his recovery. He also proved of assistance in interrogations, having an ability of understanding when someone was telling the truth or not.
Eventually it was understoot that his potions were slowly poisoning Odin. Tarakis and Thanos used Odin's weakness to steal a mystical artifact from him which would assist in Thanos' plans of bringing death to the universe. He later joined Mangog in combat against Thor and Firelord. Tarakis took a monstrous form which fired energy blasts stunning his opponents. He managed to incapacitate Firelord and encase him in ice. Mangog took care of Thor.
Later the two incapacitated foes returned and Firelord blasted Tarakis to pieces before the alien had time to react.