Seeking revenge after his wife Mary was killed by the demon Azazel, John Winchester became a hunter and raised his two sons to fight the supernatural. John disappears early in "Supernatural", and the first season revolves primarily around Sam and Dean trying to find him. Morgan was also filming episodes of "Grey's Anatomy" while the first season of "Supernatural" was under production, and future appearances of the character were hindered by his busy schedule. While Morgan's portrayal has been praised, fans and critics were generally frustrated at the character for keeping so many secrets.