The Winchesters and Gabriel

Sam and Dean's relationship with Gabriel the Archangel.

Background
Sam and Dean Winchester were brothers destined to become the vessels of Lucifer and Michael respectively, so the latter could complete their rivalry and argument on Earth during an event known as "The Apocalypse". Gabriel was Lucifer and Michael's younger brother, who had fled Heaven the last time the two brothers fought as he could not bear to witness such horrors.

Although Gabriel was aware of Sam and Dean's destiny, he was unwilling to partake in the event and instead he appeared to them under his guise of a deity known as The Trickster.

Tall Tales
Posing as a janitor at Crawford Hall university, Gabriel began punishing various people on campus who were known for misbehavior, by serving them their "just desserts". The first victim, Professor Arthur Cox, was tricked into letting a girl into his office (something he often did) and fell out of his window after she revealed her mutilated face.

Sam and Dean came to investigate by posing as electricians. Gabriel lets them into the professor's room and tells Sam (while Dean munches on nuts) about the professor's tendency to pick up girls, and on the night of his death, he saw a girl go in but never come out. Gabriel jokes around with the brothers, who seem delighted in his presence, before they leave.

As more and more victims experience weird occurrences that don't always end up in death, Sam and Dean request Bobby Singer to come over and help them out. Prior to that, Gabriel had begun pulling pranks on Sam and Dean causing the brothers to fight each other. Bobby deduced that they were dealing with a Trickster, leading Sam and Dean to suspect Gabriel.

Sam investigates Gabriel's locker room to find magazines about aliens, which had apparently abducted a school boy earlier. This confirmed Sam and Dean's suspicion. In an attempt to trick Gabriel into thinking that the two of them were not on good terms, Sam and Dean argued outside the university while Gabriel watched. Dean then entered the theater to find two of Gabriel's illusions, posed as scarcely dressed women, offering themselves to him on the stage.

Gabriel told him that the women were a peace offering, in exchange for Dean allowing Gabriel to skip town since he did not want to hurt them. Although Dean was visibly tempted, he declined letting Gabriel leave, and revealed the truth; he and Sam did not argue, but Sam and Bobby had gone to retrieve a stake dipped in the blood of one of Gabriel's victims in order to kill him. Gabriel was impressed, but since Dean refused to make a deal, Gabriel crafted more illusions and had them attack the trio as he watched delightfully.

Unfortunately, Dean managed to stab him in the heart with a stake, and Gabriel died while his illusions dispersed. After the brothers had left, Gabriel was revealed to have survived the encounter simply because a fake one had been in the theater the whole time.

Mystery Spot
As Dean's crossroads deal reaches its deadline, Gabriel comes to the belief that Sam needs to learn how to let go of Dean. He believes the younger Winchester is obsessed with his brother, which a vulnerability at the same time. Although his motives can be considered good and his reasoning sound, Gabriel's methods were anything but.

After Gabriel dumped Professor Dexter Hasselback into a wormhole to prove to the man that wormholes existed, Sam and Dean arrived at the professor's last known location to investigate his disappearance. From the moment they woke up, the brothers had been trapped in a time loop which would repeat itself constantly. Each day, Dean would suffer random deaths despite Sam's attempts to keep him safe. The lesson was to teach Sam that he was going to lose Dean anyway, so he should just let go.

Sam was distraught, becoming increasingly frustrated with the repeated Tuesdays, but he also grew well accustomed to his surroundings, and recognized when one of the customers in a diner had a different flavored syrup on his pancakes. Sam confronted the man, who revealed himself to be the Trickster they thought they had killed nearly a year before.

Gabriel admitted that he enjoyed killing Dean, but he also wanted Sam to lose his obsession with Dean. Threatened with a stake, Gabriel appeared to give in to Sam's demands and freed them from the time loop. However, by the next day, Dean was shot dead and the day did not repeat itself. Sam lived in what appeared to be the real world and spent months trying to get his hands on Gabriel. The lesson grew tiring for the archangel, who lured Sam to his location so he could try and convince Sam point blank the meaning behind his lesson.

Sam did not listen, acting like "a brick wall" in Gabriel's own words. Gabriel gave up, and finally freed Sam from his continuous nightmare, either by reviving Dean or freeing Sam from a time loop. Dean woke up with no recollection of the events.

Changing Channels
It had been approximately two years since Gabriel confronted the Winchesters, but things had become personal since destined Apocalypse was above them and Gabriel was to witness once again a fight between his brothers. Longing for the fight to end swiftly so he would not have to endure it, Gabriel pulled his usual pranks on various people to lure Sam and Dean to his desired location, before sending them into TV land.

Dean's obsession with the Dr. Sexy series enabled him to figure out who Gabriel was posing as. Gabriel pretended he simply wanted to mess with Sam and Dean, ignoring Sam and Dean's attempts to get his help. He insisted that if the brothers wanted to talk, they should survive the next 24 hours. Sam and Dean were forced through more television-based universes, until Castiel broke in and tried to warn them of the person they were dealing with, hinting that it was not a Trickster.

Gabriel made an effort to lock Castiel away to keep his identity hidden, which angered Dean. Being far stronger, Gabriel pinned Dean to the wall and demanded the brothers to "play their roles" as they were already doing in TV land. He blamed Sam from bringing about the Apocalypse by freeing Lucifer, and assured them that he was not working for either of the archangels. However, Gabriel intended to keep them locked up in TV land until they agreed to say "yes".

Unfortunately, the brothers learned from Gabriel's behavior and his encounter with Castiel that he was most certainly an angel. Trapped in holy fire, Gabriel admitted the truth: he was an archangel, and he was trying to hasten the inevitable battle. While he insisted that nothing could stop the fight from happening, Dean argued that Gabriel was simply being a coward by not standing up to his family. Dean freed Gabriel from the trap, leaving the archangel soaked and forced to contemplate his next move.

Hammer of the Gods
Sam and Dean fell into a trap set up by a group of pagan deities, who wanted to use them as bait in order to overthrow the archangels now messing with the world. Gabriel felt obliged to rescue them, but his attempt to do so failed when the leader of the group and his former fling, Kali, knew who he was and made an attempt on his life to prove to her associates that archangels could be killed.

However, Dean discovered the real Gabriel hiding in his Impala. The three were currently trapped due to Kali holding them hostage through possession of blood vials. Gabriel's attempt to retrieve them failed, so he urged Dean to do it. Dean did not, and instead he urged Gabriel to stop being afraid. Lucifer was on his way and Dean needed Gabriel to be brave enough to confront him. Dean could tell that Gabriel cared for the pagan deities, and when Gabriel did not verbally agree to go back inside, he acknowledged Dean's words.

When Lucifer had killed all but one pagan deity who was Kali, Gabriel arrived and saved her. He helped Kali and the brothers leave the hotel as he stood, for the first time in eons, in front of his older brother. By then, Gabriel had passed on a DVD to Sam and Dean containing the secrets about the Four Rings of the Horsemen. It was this gift that, despite Gabriel's death at Lucifer's hands, enabled the brothers to open the Cage and throw Lucifer (as well as Michael) into it, thus ending the Apocalypse and stopping the fight.

Gabriel was, alongside Crowley, Sam and Dean's most valuable new ally at the time.

Trivia

 * Gabriel is the first archangel and primordial entity Sam and Dean met. He was also the youngest out of both.
 * Gabriel is the only archangel to date to become Sam and Dean's ally and stay that way.
 * Lucifer had briefly become allies with Sam and Dean in order to fight The Darkness alongside God. This alliance was broken after God abandoned Lucifer for a second time.
 * Gabriel is one of very few angels overall to ally himself with Sam and Dean, another is Joshua.
 * Gabriel's behavior towards Sam in Season 3 may reflect his own past, being forced to abandon a beloved older brother despite his desire to keep them. This maybe a reference to Lucifer, who became - in Gabriel's own words - "a big bag of dicks" following his first imprisonment in The Cage.