This, despite the stress and harm it causes his character, allows him to develop an independent will as the series progresses and helps the show address topics related to free will.

Because merely perceiving his actual form typically results in blindness,[4] he takes a human host – James "Jimmy" Novak,[5] a "devout man" who prayed for it – to communicate with Dean, and tells him that he has been brought back because God has work for him.

[6] Castiel continues to appear throughout the season, at one point sending Dean back in time and later tasking him and his brother Sam with stopping witches from breaking another seal.

With Sam closing in on Lilith, Castiel and Zachariah imprison Dean within an idyllic waiting room, where he will be made comfortable until the time comes for him to play his role in stopping the Apocalypse.

[11] However, Castiel later returns – still in Jimmy Novak's body – in the fifth-season premiere, "Sympathy for the Devil", killing two fellow angels in order to save Sam and Dean.

[12] He remains on Earth hunting for God, although acquires a cell phone so that the Winchesters can call for his aid when dealing with particularly challenging cases, such as their discovery of the Antichrist or their latest confrontation with the Trickster (who is revealed to be the lost archangel Gabriel).

When relayed to Castiel, his hopes and faith are shattered,[16] leading him to drink heavily in the subsequent episode "99 Problems" when Sam summons him for answers about the actions of the people in a town.

Later, he carves a banishing sigil into his own chest and activates it in the presence of multiple angels in order to clear the way for Sam and Dean to attack Zachariah and save Adam.

Despite his lack of power, he is able to defeat the Horseman Pestilence using what appears to be what little is left of his angelic strength, and assists Bobby and Sam in preventing nationwide distribution of the Croatoan virus.

[18] In the fifth-season finale, "Swan Song", Castiel loses faith after Sam fails to overpower Lucifer when he possesses him and suggests they get drunk and wait for the end to come.

A year after the Apocalypse, Castiel returns to Earth in "The Third Man" to get Sam and Dean's help to find the Staff of Moses, which, along with many other weapons of Heaven, has been stolen during the war.

After trapping Balthazar within a ring of ignited holy oil and forcing him to restore the souls he has taken, Castiel sets him free, claiming his debt has been paid off.

At the end of the episode Castiel explains to Sam and Dean that the celestial war is not going well for him and he would rather be on Earth with them, but leaves anyway to continue fighting, but promises to take care of Crowley's captured monsters first.

In "Mommy Dearest", it is discovered that there is a possibility Crowley may have faked his death and might still be alive; suggesting that perhaps Castiel had burned the wrong bones by mistake.

In "The Man Who Would Be King", it is revealed that Castiel was the one who partially raised Sam from Hell, though due to the complication of the cage it was impossible to retrieve his soul, and that he has made a deal with Crowley in a desperate attempt to win the war.

While talking to Dean, who unsuccessfully begs him to give up the power, Sam sneaks up behind them and attempts to kill him with an angelic blade by stabbing Castiel in the back, but it has no effect.

He later escapes with the aid of an army of angels sent to rescue him – having initially remained behind as penance for his actions to stop a duo of Leviathans that were trying to attack Dean and Benny as they left Purgatory – but the other angels not only erase his memory that they were responsible for his escape, but also erase his memory of their subsequent 'check-ins' to discuss the Winchesters' actions, with Castiel forced to tell them about the Winchesters' progress in the search for the tablet.

Castiel, having listened to Sam's speech about running from reality as well as Fred, decides to return to Heaven to try to make up for what he did, but is forbidden by Naomi, the angel who ordered his rescue.

When Castiel contacts the Winchesters, however, Dean tells him to leave Hael and make his way the Men of Letters bunker where he will be safe from the angels hunting him.

After being contacted by Dean, Castiel, now wearing a new suit and trench coat and driving a stolen car as he can no longer teleport, returns to the bunker where he comes up with the plan to have Crowley help expel Gadreel from Sam.

Although Claire initially resents Castiel's return to her life, she comes to accept him and the Winchesters after they save her from being sold as a prostitute by a man she believed had been helping her.

Seeking to help Dean find a cure for the Mark of Cain, Castiel breaks Metatron out of Heaven and removes his Grace so that the Winchesters can interrogate him.

The Cosmic Entity, who rules this realm, is annoyed by Castiel's being awake and attempts to use his own memories and insecurities against him to make him fall back asleep forever.

Castiel attempts to assist Sam in healing a traumatized Gabriel, who is actually alive, after faking his own death and being captured by Asmodeus, who tortured him and extracted his grace for power for years.

She then tells Castiel that due to the fact that there are only a dozen or so angels left alive after the various wars and purges of recent years, Heaven is at risk of falling apart and having the billions of souls residing there sent back to Earth as ghosts, which would cause untold destruction and chaos.

Michael is eventually apparently expelled from Dean, but Jack later dies as a result of his angelic heritage being at war with his human nature now that his grace has been stripped.

[9] Throughout his appearances in the fourth season, he also seems to, at the very least, come close to expressing regret, hesitance, and anger several times, and has once quietly laughed at a joke Dean made in "It's the Great Pumpkin, Sam Winchester".

[27] Having lost his connection to Heaven in the fifth season, Castiel's humanization seems to have quickened by the episode "Free to Be You and Me", as he appears extremely anxious while in a whorehouse, is visibly distraught when asking Dean for help, and refers to the Archangel Raphael as "my little bitch".

However, parts of Castiel's original personality are still shown with him still being happy to help Sam and Dean out and still knowledgeable about various supernatural things, but not willing to actually fight anymore even when his life is threatened.

[41] TV Squad ranked him as the top reason to watch the series, noting the "slightly awkward, frighteningly precise angel... has done an amazing job of selling the underlying menace and vengefulness of God's most heavenly creatures.