Deanmon

Dean is resurrected as a demon at the end of season 9.

After Dean accepts the Mark of Cain from Cain himself in season 9, it begins changing him, granting him supernatural powers, ramping up his bloodlust, and making him addicted to using the First Blade. When he is killed by Metatron in 9.23 Do You Believe in Miracles?, the Mark resurrects him as a demon, with the additional bonus that he is immune to exorcism as he is not technically possessing his body but its natural 'owner'. He is later cured by Sam in 10.03 Soul Survivor though he still possesses the potential to become a demon again as he still has the Mark of Cain.

UPDATE: Dean can no longer become a demon (from the Mark of Cain) as Rowena removes it using the Book of the Damned in 10.23 Brother's Keeper.

The term Deanmon was popularized by the CW promo "Deanmon Rises" which aired in September 2014 ahead of season 10.

See also

• Demon!Dean