Gwen always the goodness self. She have a heart of gold. Always there for others. A perfect match for Arthur and a perfect queen.
Guinevere ("Gwen") (portrayed by Angel Coulby) enters the story as Morgana's personal servant, and eventually becomes the Queen of Camelot.
At the start Morgana describes Gwen as "the most kind and loyal person you would ever meet". She first notices Merlin when he stands up to Arthur when Arthur is taunting a servant. When she introduces herself she admits that she thinks Merlin is brave and a real hero, and it's the beginning of an attraction that develops over series 1. In "The Mark of Nimueh", Merlin makes her laugh and she admits that she likes that. She kisses him in "The Poisoned Chalice" however, Merlin only loves her platonically, and Series 2 sees them as good friends with Merlin seen to be a strong advocator in her blossoming relationship with Arthur. Merlin trusts her and often enlists her help in various ventures, most notably in Lancelot's quest to become a knight in "Lancelot", hiding Arthur in "The Once and Future Queen" and in saving Gaius in "The Witch finder". Gwen is imperative in saving Arthur's life in "Sweet Dreams", and it is due to Merlin's convincing that she agrees to help. Due to Gwen's status she has a tendency to be subservient, but she is seen to not be afraid of standing up for her beliefs and speaking her mind; a trait admired by most around her, particularly Arthur.
She initially has little interaction with Prince Arthur and describes him as a bully, questioning the mind of whoever would marry such a person. However, following her father's death and her friendship with Merlin, Gwen's view of Arthur begins to change. Gwen has openly expressed her faith in Arthur's ability to triumph over the odds and lead the people into a new age of a peaceful Camelot. Most notably, she did so as she tended to an unconscious Arthur in the Series 1 finale. She became embarrassed however the following morning to find out that Arthur had heard what she had said. "The Once the Future Queen" again displays Gwen's ability to stand up to Arthur as when he stays at her house pretending to be a commoner, Gwen becomes aggravated when Arthur is nothing but rude to her. Affected, Arthur tries to be more considerate towards Gwen (offering to make dinner etc.), and ultimately kisses her before he goes to joust. Arthur explains at the end of the episode that his father would never approve of their relationship, something which Gwen understands.
In "Lancelot and Guinevere", Gwen is abducted, only to be reunited with her old flame, Lancelot. She states that he is everything right in the world and didn't know she could feel as strongly as she could for him. They share a kiss when it seems Lancelot will not return from fighting the bandits. When Arthur arrives to save Gwen, he realises that the flame between Gwen and Lancelot has been reignited, and he is hurt and claims that he only came because Morgana made him. Gwen appears to feel guilt over Arthur's obvious reaction and hurt too because now he is denying that he has 'feelings' for her. Lancelot guesses that Arthur loves Gwen and so he leaves at the end of the episode so they can be together. She returns to Camelot with Arthur and Merlin, where she is reunited with Morgana.
Gwen continues to be charmed and impressed by the changing nature of Arthur as the series continues, witnessing him blatantly defy his father's orders when told to impose unnecessary taxes. When she visits Arthur to thank him for his kindness, she finds him doubting his father's love for him. Gwen advises him that Uther cares greatly for him and that Arthur will become one day a great King. Gwen restores his confidence by telling Arthur he has a good heart and shouldn't change for anybody. Apart from Merlin at times, Gwen seems to be one of the few people who Arthur respects the opinion of. Despite past problems and outside interference, their relationship continues to flourish.
When other kings from rival kingdoms came to Camelot to sign a peace treaty, one of them brought his daughter Vivian. King Alined used magic to make Arthur and Vivian fall in love. Around this time, Gwen started to regain faith in Arthur's feelings for her, and was left heartbroken when she saw Arthur with Vivian. Gwen kissed Arthur to break the enchantment he was under. Arthur waited in Gwen's house for her, where he apologized for his enchanted actions and that she was the only woman he loved. Gwen accepted this, but also realizes that she cannot be Arthur's queen. Arthur refuses to believe their relationship is impossible and promises things can change.
Towards the end of Series 2, Gwen and Arthur became slightly more comfortable around each other in public places. When Arthur was injured trying to save her from the Great Dragon, they shared a tender moment in front of many (although Gaius was the only one who noticed) as Gwen saw to his wound. She tells Gaius when he notices her worry that they can never be, but Gaius comforts her by telling her to never underestimate the power of love. When Arthur returns from fighting at the end of the episode, Gwen runs to him and hugs him tightly. She whispers that she thought she'd lost Arthur, her open affection surprising him slightly. They embrace, not caring about Merlin and Gaius being there, and happily walk back to the castle together.
With Gwen's relationship with Morgana having cooled after Morgana's return to Camelot and her new allegiance to Morgause, Gwen has begun to spend more time with Merlin, assisting him when he was accused of sorcery while Gaius was possessed by a goblin. During a recent adventure where Gwen's estranged brother was captured by Cenred as a hostage to force her to lure Arthur into danger, the two appeared to begin a secret relationship, Arthur not-so-directly telling Gwen that he loved her, the two later kissing in private before Arthur departed on his quest to recover the trident of the Fisher King.
The "Queen of Hearts" episode is purely about Arthur's love for Gwen. Having had a vision of Gwen as Queen of Camelot, Morgana sets them up on a picnic outside Camelot only to bring Uther to catch them and banish Gwen from ever seeing Arthur. When Morgana realises this will not stop their relationship, she plants a bag under Arthur's pillow and suggests that Gwen has enchanted Arthur to make him act this way, prompting Uther to sentence Gwen to be burnt at the stake. Fortunately, Merlin is able to clear Gwen of this crime by using an aging spell to give himself the appearance of an elderly sorcerer who enchanted both Gwen and Arthur to cause chaos in Camelot, the two subsequently agreeing to keep their feelings secret until Arthur is king and can change the laws that currently prevent them from being together.
During Morgana's subsequent conquest of Camelot, Gwen feigned continued loyalty to her mistress in order to wait for an opportunity to assist Arthur, eventually managing to sneak Sir Leon out of Camelot so that the two of them could join Arthur and his small band of knights. Although Gwen was briefly reunited with Lancelot, she now appears more secure in her relationship with Arthur, kissing him before he departed for the raid on Camelot, the two sharing another kiss in the courtyard after the battle when Gwen rode into Camelot alongside the new Knights of the Round Table.
In the episode "Lancelot du Lac", Morgana brings Lancelot back from the dead when she hears that Arthur intends to marry Gwen. Arthur asks Gwen, 'Would you do the honour of becoming my wife?', But when Lancelot returns to Camelot, Gwen betrays Arthur when he sees her kissing Lancelot. Gwen, unknown to Arthur, was under the spell of a bracelet given to her by Lancelot from Morgana who intended to stop the marriage. Arthur banishes Gwen from Camelot and Lancelot is said to kill himself. It is implied that she will return in the synopsis of the episode "The Hunter's Heart".
She does not return to Camelot in this episode, but she over hears Morgana's plans to kill Arthur. She tells Merlin she can never face Arthur again leaving Merlin to tell Arthur of Morgana's plans. Arthur's feelings for Gwen are once again revealed when he finds the ring he gave to her, under the influence of Merlin and admits that he still loves her.
In "The sword in the stone", Arthur and Merlin ran away to Merlin's home town where they met Gwen again and after seems to forgive her. Arthur didn't forgive Gwen fully but when he saw Isolde die he didn't want to lose her therefore Arthur openly forgives Gwen and this time he says, 'Will you marry me?', and finally she is crowned Queen of Camelot.
In "The Dark Tower" of season five, Guinevere is brainwashed by Morgana through mental torture—letting her see visions of people she cared about laughing maniacally at her and telling her she can trust no one but Morgana herself. Under the command of Morgana she is made to betray Arthur in the next episode. In the episode "A Lesson In Vengeance", Gwen is horse riding with Arthur and Merlin when Arthur's horse is spooked by a minor explosion caused by magic. The servant in charge of looking after the castle's stables is suspected. When he is imprisoned and sentenced to death, it is later revealed that Gwen was the one responsible. When the Tier finds this out, Gwen stabs and kills him. King Arthur is poisoned by a mysterious culprit and Gwen tells Camelot that Merlin is responsible. Merlin is later thrown in the dungeons. Gaius later finds out that Gwen has been put under the control of Morgana and vows to help Merlin uncover their betrayal to Arthur. Gwen is later told by Sir Leon that if the King dies, the closest heir to his throne is her and she will be the ruler of Camelot. Finally Merlin and Arthur are able to free Gwen using a magic pool. In the final episode after Arthur is wounded in battle he sends the royal seal to Gwen via Gaius, hoping she will succeed him. When he dies Gwen becomes ruler of Camelot.