The tyrannical leader of the demon world, Azazel first appears in the pilot episode. His earliest chronological depiction occurs in the fourth season finale, "Lucifer Rising". Having spent years searching, Azazel finally located the doorway to Lucifer's prison in 1972. The fallen angel tasked him with freeing the demon Lilith from Hell—she is needed to break the 66 seals holding Lucifer captive—and to find him a "special child". By the following year, he began making demonic pacts with young individuals; in exchange for a wish, he would be allowed to enter their homes ten years later. Azazel eventually comes across Mary Campbell, the future mother of series protagonists Sam and Dean Winchester. After taking possession of her father, he kills her mother and stabs himself to kill his host. Mary's fiancé, John Winchester, is the demon's next victim. However, Azazel makes his usual offer, giving her the chance to resurrect John; she reluctantly agrees.

In 1983, Mary discovers Azazel standing over baby Sam's crib; he had been feeding his blood to the infant. Upon being interrupted, the demon pins her to the ceiling, slashes her stomach and causes her to burst into flames. Mary's death inspires John to dedicate his life to hunting down Azazel, at the same time training Sam and Dean to hunt supernatural creatures. As revealed in the fifth season finale, "Swan Song", Azazel sent demons to possess important people in Sam's life, secretly manipulating him as he grew up. However, Sam eventually leaves the life of hunting to attend college. Azazel orders the assassination of Sam's girlfriend Jess, whose death prompts Sam to return to hunting after leaving the life to attend college.