Crowley is introduced mid-way through Season 5 in the episode "Abandon All Hope...", having first been mentioned near the end of the previous episode, "The Real Ghostbusters", when the series' protagonists Sam and Dean Winchester learn that Crowley—not Lilith, as was previously believed—had been the one who took The Colt from Bela Talbot in the Season 3.
Despite ever-increasing animosity between himself and the rest of the group, Crowley helps Dean recover the final ring from Death.
Gavin provides the location of Crowley's grave, and the Winchesters dig up his remains and threaten to burn them, which would end his existence, if he does not return Bobby's soul.
[12] In response, Crowley orders his demons to refrain from attacking Sam and Dean, to allow the Winchesters to wipe out the Leviathans.
Despite the deal, Crowley gives Sam and Dean his real blood, resulting in Dick's death and the Leviathans' plan unraveling.
[19][20] In "Taxi Driver", he attempts to sabotage the second trial Sam and Dean are trying to finish, by dragging the deceased Bobby's soul back to Hell where he had it trapped earlier through use of a reaper working for him.
[26][27][28] He is set free in the episode "Road Trip" when Dean lets him go to help him in saving Sam, and immediately starts trying to defeat Abaddon for rulership of Hell.
[31] Ultimately, though Crowley and his time-displaced son Gavin fall into Abaddon's clutches in "King of the Damned", he is able to aid Dean in killing her by giving him the location of the First Blade and discreetly tipping him off to her trap for him and Sam.
Crowley's increased humanity prompts him to keep Gavin alive in the present to spare him the death he had experienced in his own time, and to reconcile much of their mutually hateful relationship.
In "Soul Survivor", Crowley returns to rule of Hell, executing Abaddon supporters, but finds his time with Dean to be causing him problems.
Rowena was a terrible mother who ended up abandoning him at age eight and never returning despite promising to, something Crowley holds a great deal of resentment towards her for.
Rowena plots against Crowley, making him have nightmares of being attacked by his demons and spying on a meeting with the Winchesters where they ask him for the First Blade back to help get rid of the Mark of Cain.
Crowley believes Rowena's lies about Guthrie and informs the Winchesters he will keep the Blade until they are ready to use it to remove the Mark.
He attempts to 'raise' Amara- a soul-draining young woman who was 'born' when the Mark was removed from Dean- for his own ends, but she soon proves too powerful to control.
Attempts to battle Lucifer and the Darkness eventually fail, but they are able to stop the threat by convincing Amara to reconcile with God, her 'brother'.
Working with Castiel and Rowena, Crowley is able to force Lucifer to keep 'jumping' between vessels, eventually exorcising him from the body of the President of the United States and trapping him back in Nick.
Lucifer eventually escapes and apparently kills Crowley, something the Winchesters learn about from the British Men of Letters.
Crowley's death completes the spell, but Lucifer is able to kill Castiel before he is trapped in the alternate reality with Mary Winchester.
However, executive producer and current series showrunner, Jeremy Carver, explained that Crowley "actually doesn't care for [Hell] much", in contrast to Abaddon, his challenger for the crown in Season 9.
On this topic, executive producer Robert Singer said that Crowley's secret enjoyment of his temporary sense of humanity influenced the character throughout the ninth season.
[40] In an exclusive interview with Michael Ausiello on July 15, 2010, series creator Eric Kripke confirmed that Crowley would return in the show's sixth season.
"[36] Carver, too, enjoys the character, stating, "He's pure evil, but, in an odd sort of way, we find him likable.
"[37] When discussing plots that had been either set up or not resolved by the end of Season 9, Knight cited the developments in Crowley's story, questioning what the character plans to do with the demonic version of Dean he beckoned to in the closing moments of "Do You Believe in Miracles?"
"[44] On io9, Charlie Jane Anders praised Sheppard's "impeccable comic timing, and his ability to sell an entire scene with afew [sic] well-chosen facial expressions.