Dean Winchester and the demon Ruby have never been friends, nor have liked each other. Regardless of their hostility towards one another, they have saved each other's lives on occasion and at one point held a temporary mutual trust. When she comes between him and Sam, due to Sam's demon blood drinking problem, Dean's distrust of her intensifies. When her betrayal comes to light, Dean is the one who kills her, with Sam's help.
Although Sam is the first to meet Ruby, he tells Dean about her, after she repairs the Colt for them. Following his hunter instincts about demons, Dean is furious that Sam let the demon live, and trust her. Dean believes deep down that all demons are bad ones. The two finally meet in Malleus Maleficarum when Ruby stops the Impala to give them a warning.
|“||Ruby? Why do you want us to win?" "Isn't it obvious? I'm not like them. I don't know why. I wish I was, but I'm not. I remember what it's like. What what's like? Being human.||”|
— Dean and Ruby
in Malleus Maleficarum
Later on, Dean is coughing up blood, and Ruby bursts into the motel he is located in. Dean tells her to get into line to kill him, and Ruby responds by grabbing him and shoving Dean onto the bed. Followed by forcing Dean's mouth open and pouring a strange liquid down his throat. Once done, Ruby tells Dean to stop calling her "Bitch". When Dean is able to breathe again, and asks what it was. Ruby answers it was witchcraft, and leaves, leaving Dean stunned that she saved him. When Dean and Sam are pinned by Tammi, Ruby comes in telling Tammi she want to join forces again, and that she has been lying to the brothers, and Dean believes this. Ruby's plot is found out, and Tammi overpowers Ruby. Then she reveals that Ruby used to be human once, which surprises Dean. When Tammi gets distracted, Dean quickly grabs Ruby's Knife and stabs Tammi. After the fight, Dean gives Ruby back her knife and Ruby tells them to get lost.
Outside the motel, Ruby comes to Dean. He asks her if it was true about her being human once. Ruby answers Yes, and that in fact every demon she has ever met, used to be human. Dean begins to wonder if it will happen to him, and Ruby confirms it will, because that is what Hell is, it makes you forget who you were. Dean tells there really isn't any way to save him, which she confirms. Dean asks her why she lied to Sam, and Ruby tells him she needed a way to get Sam to speak to her. Then Ruby asks for Dean's help with Sam. Help her get Sam ready for the coming Demon war, and life without Dean.Dean sees Ruby again in Jus In Bello. As they prepare for a demon onslaught, Ruby comes in. Trusting her a bit more this time, Dean doesn't treat her the same as he did when they first met. In the main part of the jail, Dean asks her how many are out there, and Ruby tells him about 30. Then Ruby reveals who is behind this; Lilith. When Ruby finds out that the Colt is missing, she tells them of another plan, which involves killing the virgin, Nancy. This surprises and angers Dean. He instantly refuses to go through with the plan, and his opinion of Ruby changes again. So with no one agreeing with her plan, Ruby leaves. Much later, Ruby comes by their motel room, and gives them hex bags to hide them from Lilith.
As days come down to hours, Dean refuses to call Ruby for help when Sam suggests it in No Rest For The Wicked. Dean points out to Sam that she is Miss Universe of lying skanks, plus she lied to Sam about saving Dean and didn't tell them that Lilith has his soul. Dean further points out that Ruby could be working for Lilith. By now, any trust Dean had for Ruby is gone. It is further proved when he walks in when Ruby and Sam are talking. He telling Ruby he is not letting Ruby teach Sam anything, and that Ruby is going to give Dean her knife. Ruby points out that Sam is powerful, but Dean cuts her off and points out to Sam that Ruby is using him. Ruby gives up trying to prove herself to Dean. As Dean walks away, he quickly turns around and punches Ruby. She in turn attacks back, and beats up Dean. Still standing, Dean shows that he managed to grab her knife, and trapped her in a devil's trap. Dean leaves Ruby there screaming at him.As they head for Lilith, Ruby manages to break free and confronts Dean. She pushes him against a fence, and threatens him to give back her knife. Ruby does join in and help them. They make a mad dash to the house Lilith is located in. As they pass, Bobby Singer turns on sprinkler system filled with holy water. As they watch the demons back away, Ruby comments that Lilith probably know they're here now. Unfortunately, Lilith takes over Ruby's vessel, and sends her hellhounds at Dean, killing him and sending him to hell.
|“||Well, you got a lot of nerve showing up anywhere near me." "I just have some info, and then I'm gone.||”|
— Dean and Ruby
in I Know What You Did Last Summer
Dean unknowingly sees Ruby again in Sam's hotel room, but she plays dumb and pretends not to know who he is, and acts like a one-night stand to his brother. Although, it is revealed in Metamorphosis that she is alive to Dean. With this information, he attacks Ruby, and attempts to kill her, but Sam stops him. Dean manages to break free though and goes at Ruby again, but this time Ruby overpowers him, and pins him to a wall by his throat. She stops though, when Sam tells her to and leaves to take the man to the hospital. Dean is surprised, but angry to see Ruby back, and teaching Sam the very thing Dean didn't want Sam to do.
Dean isn't too happy to see Ruby when she pops into a bar in I Know What You Did Last Summer to give them a tip. She tells them about Anna Milton, a girl who demons are after. Dean lies saying they are working a job, to avoid looking into what Ruby suggested. But they do look into it, and find Anna in a church. Soon after they find Anna, Ruby comes telling them they have to move, Dean believes that Ruby led them here. Ruby quickly points out that she didn't bring them there, but the demons followed Sam and Dean here. When Ruby realizes its' too late to leave, she tells Sam to use his powers, much to Dean's disapproval. Once they escape, Ruby soon contacts them to where she is with Anna. When they meet up with Ruby, Dean thanks her for saving Sam, but trusts her a bit more than he used to. She is amused by Dean's change in attitude to her and tells him not to push himself.
In Heaven and Hell, Dean saves Ruby from Uriel when he is about to smite her. Once they have escaped the angels after Anna, they go to Bobby's Panic Room to protect Anna. There Ruby gives Dean hex bags to hide them from angels and demons. Dean thanks her for this. Dean's growing trust for Ruby leads him to laugh after he sees her sitting next to Anna and to trust her with the plan to get both the angels and demons all in one spot.
Although that trust shatters when Dean realizes what she did to Sam. How she got him addicted to demon blood. So he follows Sam right to her in When The Levee Breaks to the hotel room. When Sam leaves, Dean goes into the room and attacks Ruby. Sam stops him and lets Ruby escape.
In Lucifer Rising, all of Dean's suspicions of Ruby are proven correct when she notices him at the church and telekinetically keeps him out of a room so he won't stop Sam from killing Lilith to free Lucifer. After Dean breaks into the room, Ruby tells Dean that he's too late to stop it and he states he doesn't care. Dean then finally kills Ruby with the her knife with the help of Sam restraining her from behind.
In The French Mistake, Dean is surprised to find that Sam is married to Ruby. When he first sees her he calls her Ruby, but she rolls her eyes, sighs, and asks when he is going to stop calling her that. When she goes to kiss Sam, a stunned Dean looks away. For him it's weird to see his old enemy alive and married to his brother. Dean realizes that she is the actress who played Ruby, Genevieve Padalecki and she believes he is Jensen Ackles who portrays Dean.