Dean originally believed Lucifer to be a fairy tale until Castiel told him otherwise. Dean met Lucifer for the first time when Zachariah transported him to an alternate future in the year 2014. This Lucifer possessed Sam which horrified Dean as Lucifer casually greeted him. He chose to spare Dean, right after killing Dean's future counterpart. Lucifer attempted to get Dean to understand him, but Dean bit back saying that he was like every other monster Dean hunted, the only difference being the size of his ego. Lucifer ended their conversation with assuring Dean that they would "always end up here".
In the present, Dean sought to kill Lucifer by using the Colt, though the plan failed and Dean was left with relying on Sam's own plan of saying "yes" to Lucifer in order to send Lucifer back to his Cage. Dean watched as Lucifer abandoned his previous vessel for Sam, and then took Sam for his own.
At Stull Cemetery, Dean interrupted Lucifer's battle with Michael. In retaliation, Lucifer beat Dean up, calling him "a pain in my ass". Dean called to Sam as he was attacked and Sam eventually managed to take control of his body, and return Lucifer to his prison. A recently resurrected Castiel then healed Dean of his blood-soaked injuries.
Dean did not meet Lucifer again until about five years later, when Sam convinced him to allow him to speak to Lucifer. Unfortunately, Lucifer had set up a plan to escape the Cage, and despite Dean's efforts to stop him, Lucifer got out. Dean would not known of this for a time, and conversed with Castiel, unaware that Lucifer was possessing said friend. When Dean did find out, he made an effort to rescue Castiel.
Lucifer repeatedly mocked Dean over his concern for Castiel. Originally, he planned on using Dean's connection to Amara for good use, but after discovering, and subsequently obtaining a Hand of God thanks to the brothers, he ultimately chose to be rid of Dean and Sam. His effort to kill the brothers failed when Amara herself kidnapped him, an incident which he blamed the brothers for. Later on, Dean arranged a rescue mission to retrieve Lucifer, believing him to be a necessity in the war against Amara.
Once the archangel was at the Bunker, however, he began throwing a teenage tantrum at his father, forcing Dean (and Sam) to get the two to sit down and talk. Afterwards, Dean and Lucifer worked together to fight Amara, though they continued to annoy each other. Amara eventually expelled Lucifer from Castiel's vessel, much to Dean's delight, as it returned Castiel to him. However, Dean was shown to still worry about Lucifer enough to check on him when he thought Lucifer was still inside Castiel, and asked what happened to him after his eviction.
After God and Amara's reconciliation and departure, as well as after the confrontation with Toni Bevell, Dean learned from Castiel that Lucifer was still out and about and Castiel planned to capture him, something Dean offered to help with. Eventually, Castiel accepted his help and Dean traveled to Los Angeles to interrupt a concert Lucifer was hosting. Dean succeeded in chasing the guests out with gun shots fired at the ceiling. Lucifer was obviously unhappy about this, and he and Dean, Sam and Castiel got into a brief struggle, in which Dean handcuffed Lucifer.
Lucifer greeted him with mild surprise and threw him off the stage and melted the handcuffs from his wrist. Dean then bore witness to Lucifer's confession and why he was motivated to kill people randomly. Dean showed no remorse over Lucifer's sense of betrayal caused by his father's abandonment, and merely looked on in dislike as Lucifer vowed to destroy the humans in retaliation. Dean taunted Lucifer about the deterioration of his vessel, to which Lucifer agreed that Vince Vincente was wearing thin, and promptly left the vessel. Dean vowed to capture him.
Dean and Sam followed Lucifer to a church and then towards the President of the United States, who was Lucifer's next choice for a vessel. When Castiel sensed the conception of Lucifer's child, Dean remarked how he didn't know the archangel was dating. Dean later accepted help from Arthur Ketch and used his equipment to free the President from possession and send Lucifer back to Hell. Both and Sam expressed joy at finally defeating Lucifer.
Months later, Dean finds out that Lucifer had not been returned to the Cage due to Crowley's personal intervention, which has allowed Lucifer to escape a much weaker confinement. Dean angrily confronts Crowley about this, but agrees to work with Crowley again in defeating Lucifer, who is now in search of his unborn son. Dean, Sam and Castiel confront Lucifer outside Kelly's cabin, and plan to lure him and trap him inside a portal opened up by Lucifer's son. Once Lucifer is inside, Dean acts as a distraction by firing numerous bullets into Lucifer while Sam and Crowley finish the spell to close the portal.
Lucifer is unharmed, and while the spell gets completed, Lucifer is still able to escape the portal and kill Castiel right before Dean's eyes. Dean then witnesses his mother and Lucifer fall back into the portal during a scuffle between the two. The portal closes behind them, leaving Dean with a dead Castiel. Dean is quick to convince himself that Lucifer has murdered his mother and initially treats Jack with disdain since he is Lucifer's son. He assists both Sam and the resurrected Castiel in convincing Jack to choose them over his father which they succeed. He also learns from Jack that Lucifer has not killed Mary though he currently unaware that Lucifer himself has returned.
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