and Prue (Shannen Doherty) run into Assistant District Attorney Cole Turner at the site where they killed a demon, and cover their tracks. Over the course of the episode, it becomes apparent to the audience that Cole is himself a very powerful demon, pursuing Phoebe romantically and deceiving the sisters as to his true nature in order to finally kill them. In "Power Outage", Cole's superiors, the demonic Triad, learn that he may have developed genuine romantic feelings for Phoebe; Cole responds by killing them, forcing him into hiding. Meanwhile, the sisters acquire a target in the red-and-black-skinned demon Belthazor (Michael Bailey Smith); in "Sleuthing with the Enemy", the Charmed Ones discovers Cole and Belthazor are one and the same, but when Cole convinces Phoebe that he, being half human, truly loves her, she fakes his death so that her sisters Piper (Holly Marie Combs) and Prue will not hunt for him. When Cole re-emerges, causing a rift between Phoebe and her sisters, he attempts to re-ingratiate himself with his demonic peers, the Brotherhood of the Thorn, as the sisters' double agent. When Prue and Piper are both killed following a successful mission by the Source's assassin Shax (Michael Bailey Smith) in the season finale "All Hell Breaks Loose", Cole begs the Source (again, Michael Bailey Smith) to turn back time and prevent the exposure of magic. The Source agrees on the condition that Phoebe remain in the underworld under his command, though he secretly orders her to be killed. Shax attacks Halliwell Manor once more after time is reversed, but this time Leo (Brian Krause), Piper's husband who is also the sisters' guardian angel (whitelighter) is not available to heal either Piper or Prue, who lie gravely wounded.
The series four (2001-2) première "Charmed Again" reveals Leo arrived in time to heal Piper, but Prue died of her injuries, reflecting Doherty's departure from the series. Leo assisted Phoebe to escape the underworld, absconding on the Source's deal. With Prue dead, the sisters are no longer Charmed Ones, and Cole does what he can to assist Phoebe and Piper from Shax's continued attacks. Piper and Phoebe regain their full abilities—becoming Charmed Ones once again—when they discover their younger half-sister, Paige (McGowan), alongside whom they finally destroy Shax. In "Black as Cole", Cole proposes to Phoebe whilst they vanquish a low level demon. Later they find that Sykes has been mimicking Belthazor and in a bid to vanquish him Cole takes on his demonic form but has Phoebe created a potion to kill his demonic half if he can not change back. Before he can change back a woman looking to revenge his killing of her love picks up the potion and throws it at him causing Belthazor to die. In "Lost and Bound" Paige gets Cole a job as a legal aid lawyer. However he can't control his emotions and soon quits but not before the landlord who he was arguing with agrees to put the heating back on. In "Charmed and Dangerous" The Source of all Evil (Peter Woodward) breaks an aged old agreement and consumes the hollow. The Seer (Debbi Morgan) tricks Cole into consuming the hollow which allows him to assist the Charmed Ones in vanquishing the physical version of the Source.
It is confirmed that the Seer tricked Cole into becoming the new Source of Evil in "The Three Faces of Phoebe." An older version of Phoebe has turned bitter because of what he has done and warns him to save herself and states that they never got married but she can't help but think what might have been. Present day Phoebe asks him if he is hiding anything which he says he is not. The Source take over Cole completely in "Marry-Go-Round" and the Seer warns him that marrying Phoebe would be the worse thing possible as they would have a Son, the most powerful magical creature ever, but would be on the side of good to follow the charmed ones destiny. The Seer states that the only way the child will grow up on the side of evil is if Cole marries Phoebe in a dark ceremony. As the Source he puts a spell on the Charmed ones which makes Phoebe spotty and Piper and Paige to over sleep. Paige and Phoebe argue as the latter suspects the former of trying to disrupt the wedding having already made a mistake with the dress. When Paige tries to make an amends with Phoebe's spots it causes her to become invisible. Suspecting evil magic to be involved the sisters try and reverse it without success but pass the invisibility on to Paige. Cole asks the Seer to send a Lazarus demon (who she summoned to lure Phoebe to a cemetery for the purposes of a dark wedding) to attack at the wedding which causes Phoebe to call it off, thus reversing the magic on her, which had been switched to Paige. When the Charmed ones question the demon he accuses Cole of betraying him and tells them that he sent him to attack them. But before he can out Cole as the Source, Cole vanquishes him and pretends to be the Seer before teleporting and pretending to be unconscious after she attacked him.
Cole marries Phoebe in a dark wedding at the end of the episode, without her suspecting drinking her blood when a throne pricks her with the ceremony held at night with a dark priest. Cole pretends to be the perfect husband by sending Leo and Piper on honeymoon to Hawaii and buying expensive gifts such as a new car in "The Fifth Halliwheel". Paige begins to suspect that Cole is a demon again especially when she catches Cole using powers on an innocent but is not sure of what she has seen. Cole as Leo calms Paige's fears before sending the power broker demon who had already gone after the innocent after her. The Seer also puts in a plan to make Phoebe pregnant using the full moon and a tonic. The Seer and Cole create a tonic which will ensure that the child is evil when he has sex with Phoebe if she uses protection it will ensure that she falls pregnant. From taking the tonic the child will take over Phoebe's body and ensure that she remains by his side when she finds out that he is the Source. Phoebe eventually takes the tonic laced with chocolate to make the plan work. In "Bite Me" different factions have tried to become ruler of the underworld so Cole tries to make them all work together to beat good. H
owever one of the leaders encourages a group of vampires to rise up and rebel, which they do so after Cole refuses to listen to them. He almost gets exposed by Paige when she orbs in but he quickly covers this up by saying he has a migraine -hence why the blinds were down. The vampires try to turn Paige into one to get the other sisters and then over throw the source and become the new leaders.
To keep himself on top he kills the Queen after Phoebe and Piper inadvertently tell him what to do. Phoebe later discovers that she is pregnant before informing him in "We're Off to See the Wizard." Cole tries to give up the source to the Wizard after his human side becomes stro
ng and Phoebe learns through a premonition that he is a demon again but before the ritual is complete, the Seer who has manipulated Phoebe interrupt and vanquish the Wizard. Cole is crowned the source with Phoebe as his Queen. Cole faces a coup in "Long Live the Queen" when Phoebe stops the killing of an innocent. Cole demands her to make a choice and later from the Seer and him finds out that the tonic they were giving her was turning her evil. Phoebe eventually sides with her sisters and before Cole can destroy them she traps him in a crystal cage which allows the charmed ones to vanquish him. In the season finale, "Witch Way Now?", Phoebe discovers Cole is able to linger in the Demonic Wasteland, where vanquished demons go, because of his human soul. Phoebe visits him there, insisting to him that he move on to his afterlife. After she leaves, he accidentally discovers he can acquire the powers of other demons vanquished there. He becomes powerful enough to kill the beast that consumes the essence of those vanquished there and, finally, to escape. Once back in the world, he saves the sisters' lives from a witch hunter.
In the season five premiere, "A Witch's Tail", Cole returns with numerous new abilities, making him more powerful than ever. Though he still loves Phoebe, she wants to move on from him and is frustrated by his attempts to win her back. In "Siren Song," he saves the life of a young future whitelighter named Melissa in a failed attempt to impress Phoebe. When he tries to confront the demonic Siren the sisters are pursuing, the Siren puts him under her control.
Under this influence, he tries to strangle Phoebe to death before the Siren is ultimately vanquished, and Phoebe nearly dies. As a result, Cole finally understands the threat he poses to Phoebe and promises to stop using his powers, but succumbs to temptation and kills again when confronted by a sleazy landlord. In "Sympathy for the Demon", Cole is taunted by the spirit of the demon Barbas (Billy Drago), who convinces him to use a power-stripping potion, inadvertently granting Barbas his powers and a corporeal form. To stop the threat of Barbas or anyone else possessing Cole's powers, Paige strips Barbas of Cole's powers and Cole takes them back.
The sisters, however, fear that these abilities will make him evil again. In "Sam, I Am", Cole misuses his abilities and incinerates two robbers/murderers, and is later visited by two mysterious beings who identify themselves as Avatars. Neither good or evil, the Avatars offer Cole the opportunity to join their ranks and enjoy their powers; he refuses. Instead, Cole tries to provoke the sisters to kill him by sending an assassin after them, knowing that they will be able to recover thanks to their recent contact with Paige's father, whitelighter Sam Wilder (Scott Jaeck). He is distraught to learn he cannot be killed, and is pushed over the edge into insanity. Cole reverts to malevolent means of winning Phoebe back, striking at the Charmed Ones in various underhand ways over several episodes. In Charmed's 100th episode, "Centennial Charmed", Cole accepts the Avatars' offer and uses their powers to create an alternate reality where Piper and Phoebe never met Paige, who was instead killed by the Source before the Elders discovered her. In the new reality, Cole is once again Belthazor and no longer indestructible. He acts as the right-hand man of the Source and owns Halliwell Manor with Phoebe, but they are unhappy together. Paige however is accidentally brought along from the real world and teams with Piper and Leo to destroy Cole, after convincing Phoebe to join their side and turn against him.