Muriel unknowingly led Malachi to Castiel. At Malachi's place, both Malachi and Theo tortured Muriel and Castiel. On Malachi's orders, Theo killed Muriel. Malachi orders him to find out more information from Castiel. Once Malachi was gone, Theo switched sides and offered to work for Metatron, because Malachi was insane. He asks Castiel to use his "influence" over Metatron even offering to have the latter's grace restored.
Using this to his advantage, Castiel deceived Theo into thinking he and Metatron were allies and got him to remove his handcuffs. Once released, Castiel grabbed an angel blade and sliced open Theo's throat, stealing Theo's grace for himself. Becoming an angel again, Castiel smote the now-human Theo, killing Theo and his vessel.
Powers and Abilities
Theo possesses the standard powers of an Angel, even though he has fallen.
- Angelic Possession - Like all angels, Theo, was able to possess a human body on Earth, with the permission of the original owner. As he chose a body of a man around 30–40 years old.
- Immortality - Like all angels, Theo was purely immortal due to not being physical, but he could also transform his vessel into an immortal.
- Angel Blades - An angel blade could harm and kill Theo.
- Grace Removal - Removal of his grace rendered him human and he lost his angelic abilities.
- Mortality - After Theo became a human, he became vulnerable to Castiel's killing touch.
- Sage Brocklebank, the actor who portrayed Theo, starred in the TV show Psych alongside Timothy Omundson and Kurt Fuller. He also played one of Crowley's henchmen in the season 10 episodes Paint it Black and Inside Man.
- Until Season 13's Various & Sundry Villains, Theo was the last character killed by Castiel with smiting. After Theo, Castiel always used his angel blade on-screen, even when dealing with demons. After a span of over four years since he killed Theo, Castiel smote the demon Dipper in Various & Sundry Villains.
- After absorbing Theo's grace, Castiel acquired his abilities until Crowley stole Adina's grace and gave it Castiel, since Theo's grace started burning out in Meta Fiction.