Although it has been 9 years since BBC's Merlin ended, the love for the show hasn't waned. The well-written character arcs and beautiful shots of castles and battles have endured the test of time, and the series remains just as relevant and fascinating as it was back in 2008.
Each of the main characters goes through quite a dramatic metamorphosis from the beginning of their arc until their last moments in the show. Their ups and downs range from amusing to downright tragic, and their first and last lines provide a valuable perspective of their personalities and perhaps even the reason for their fate.
Percival
"Look Out!"
"Gwaine! Gwaine!"
Percival is defined by his loyalty and his quiet courage (although his famous arms are also very impressive). Under the deadly and tough exterior of a warrior, he is a kind and caring soul, and he shows himself to be a loyal knight from his very first appearance.
Called in to help Arthur and his men in the final episode of season 3, Percival saves his king from the immortal army and earns himself a spot at the Round Table as Arthur's knight. Although he comes in as Lancelot's friend, Gwaine quickly becomes his bestie. The two of them spend a lot of time together, from trying to steal chicken to attempting to stop Morgana, so it's quite fitting his final line in the show is him desperately calling out to his dead brother-in-arms.
Gwaine
"You Two Have Got Yourselves In A Bit Of A Pickle, Haven't You?"
"I Failed."
Gwaine is undoubtedly the most laid-back character in Merlin. He's also very loyal and stays true to his beliefs, refusing to treat nobles as better than everyone else just because of their birth. The very first sighting of Gwaine is in season 3, in an episode aptly called "Gwaine". He shows his bravery from the beginning by helping Arthur and Merlin out of a sticky situation, and he even gets hurt in the process.
Gwaine's loyalty to Merlin and Arthur stayed stable no matter what, even though Morgana manages to torture him so horribly using the Nathair that he reveals the truth about Arthur's location. Tragically, it's that sense of devotion that left him thinking that he failed his friends in his last moments.
Lancelot
"Run! Run!"
"Bad News. He's Still Alive."
Lancelot's tragic character arc is defined by his impossible love and the ultimate sacrifice he makes. He is introduced when he saves Merlin from the griffin and he goes out by sacrificing himself in front of Merlin so that Cailleach, the gatekeeper to the Spirit World, would heal the tear in the veil between the two worlds. He is truly selfless, both in his love for Gwen and in his loyalty as a knight, but he's also a fun and loving friend, as seen in his joking last line.
Lancelot's shade does come back under Morgana's orders, but he comes back as a simple shadow of who he really is, so his lines after his resurrection aren't truly reflective of his character.
Leon
"I Was Fearful That I Might Injure You, Sire."
"The King Is Dead. Long Live The Queen!"
Leon is without a doubt the most loyal knight when it comes to Arthur. He remains unwavering in his allegiance to his king, even when it puts his life at risk. However, he started out as a bit too devoted, as seen in his first line in the show which followed his decision to intentionally lose a jousting match against Arthur in order to keep him safe.
Leon also stays loyal to the crown after the king's death. He is a central figure during Guinevere's coronation in the series finale, being one of the knights standing in the front lines as the queen takes her seat.
Gaius
"What Did You Just Do?"
"Yes. He'll Take Good Care Of Arthur."
Merlin's destiny probably wouldn't have come true if it weren't for Gaius. The court physician's wisdom and witty remarks kept Merlin afloat throughout the show, and he was the true father figure for the boy. His timely rescues of Merlin and his vast knowledge of magic, coupled with his absolute faith in his apprentice's future, resulted in him being one of the most instrumental characters in Merlin.
Gaius spots Merlin's incredible talent from the very beginning, and he stays firm in his belief of Emrys' greatness until the end, even knowing the true nature of the prophecy and the inevitability of the king's death, as seen in his very last line in the series.
Mordred
"Help Me! Please."
"You Gave Me No Choice."
Mordred's first appearance in the show paints him as a sweet and innocent boy who is a victim of Uther's zealotry and bigotry against magic s. However, he quickly shows his true vengeful colors. His life mission is to destroy everything Arthur and Albion stand for, and he allows Morgana to manipulate him into becoming her powerful weapon against her brother.
Mordred's last line before his death in the final battle is a sign of his delusion and the fact that his extreme hatred of Arthur led him to believe that the only possible path for him is to be the cold-blooded killer from the prophecy.
Morgana Pendragon
"I Just Don't Think Chopping Someone's Head Off Is Cause For A Celebration."
"No Mortal Blade Can Kill Me."
Morgana starts off as one of the most comionate and kind characters in the show, often standing up for those who don't have a voice of their own. She opposes the persecution of sorcerers, and she isn't afraid to say it in front of Uther. However, as the series goes on, Morgana turns out to be vindictive and slowly morphs into a bona fide manifestation of evil, callously disregarding the lives of innocents if their death suits her goals.
Morgana's first and last lines are an incredibly apt representation of her character and her story, especially the brutal change from kindness to arrogance and ruthlessness. Ultimately, her inner struggle with her own magic and her final scene were some of the high points of the show.
Guinevere Pendragon
"I'm Guinevere, But Most People Call Me Gwen."
"Yes, I'm Sure He Will. I'm Pleased"
Gwen's presence in the show is characterized by her kindness and her shy nature. She's a truly good person with strongly held convictions, and she tries to stand up for those in peril, just like her lady Morgana. She treats everybody with respect, and her natural goodness shines through in her interactions. Although she does feel torn because of her love for Lancelot, she still loves Arthur deeply and cares about the future of his kingdom.
Her ending as the ruler of Albion is fitting, especially since she blossomed into a great leader after her marriage, deciding to follow Arthur into the battlefield and showing her bravery. Still, it is obvious that the loss of her husband affected her greatly, and she refuses to believe he is gone (still trusting Gaius' reassurances of Merlin's strength) until Leon confirms it.
Arthur Pendragon
"Where's The Target?"
"Thank You."
Arthur, the other side of the Merlin-Arthur coin, undergoes what is probably one of the most dramatic transformations in the show. He starts off as an arrogant bully, and his first scene makes that pretty clear. He believes that his position as the Crown Prince allows him to act however he likes, and he regularly insults those below him. His meeting with Merlin goes quite badly precisely because of his behavior.
By the end of the series, however, Arthur is a completely different person. He still teases Merlin and acts like he doesn't care, but he is a much kinder, wiser, and gentler soul nonetheless. His struggle with being a king teaches him that life isn't black and white, and he needs other people. In the end, before he es on to the shadow world, he does something he rarely does—he thanks Merlin for everything he did, finally realizing the true value of Merlin, his best friend, and completing the metamorphosis.
Merlin
"Where Would I Find Gaius, The- The Court Physician?"
"Arthur. In Sibbe Gerest. [Rest In Peace]"
Merlin spends a large part of the show as the underestimated, undervalued, and misunderstood secret savior of the day. His clumsy-but-bubbly personality at the beginning of the first season is a far cry from the tortured mourning soul seen in the final moments of the series. He dedicates his life to his king, and Arthur's death is heartbreaking for Merlin.
He remains the most loyal person in Arthur's court, and he sticks beside him no matter what, never wavering in his belief and his effort to defy the prophecy of Arthur's death. His final words to Arthur might seem like acceptance. However, as the timeline switches the modern era, it becomes apparent that he never really moved on, still awaiting the return of the Once and Future King.