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.

Does Dean become an angel?

This time it wasn't a dead Dean becoming Demon Dean like he did to close out season nine. Instead, he finally fulfilled a destiny first visited in seasons four and five of the series. He became the meat suit for the Archangel Michael…with a twist, of course.

Why does Dean Winchester turn into a demon?

Both Dean and Sam were raised in the hunting life by their father, after the demon Azazel killed their mother. ... When he was killed by Metatron whilst using the Mark of Cain, Dean returned as a demon and a Knight of Hell loyal only to himself. He was then cured by his brother using purified blood.