Kara

"It is not a crime to fight for your freedom. It is not a crime to fight for the right to be who you are. You deserve everything that is coming to you, Arthur Pendragon."

- Kara to Arthur

Kara was a druid girl who was Mordred's love interest in Series 5 episode, The Drawing of the Dark. She was executed by Arthur, which turned Mordred against Camelot.

Biography
It is implied that Kara was Mordred's childhood sweetheart at some point, though exactly when, at what age, is unknown.

It's also most likely that Kara's family (or at least close friends) were killed by Uther, as her hatred of him and Arthur is deep-set.

Personality
Following years of running, due to the persecution of those with magic, Kara was set in her beliefs, to the point of being blinded by them.

She proudly rejected all Arthur's attempts at change, seeing him as no better than his father, and accusing him of murder.

She claimed to fight for freedom, and the right to be who she was. Despite her beliefs, Kara was also dark and possibly delusional, having no problems with murdering in cold blood, seeing all connected to Camelot as evil and casualties of war.

Her hatred of Arthur was so strong that she rejected her chance of freedom, claiming to have committed no crime, despite being on trial for murder not magic.

However she also had a nicer side, and loved Mordred, to the point where she refused to betray him to Arthur.

Abilities
It is unknown if Kara was able to use magic, as we never see her doing so, and she uses a simple knife as her weapon of choice.

If she does have magical abilities, these are probably not very strong, since she kept telling Mordred to use his magic to defend them rather than doing anything about it herself, which is odd given that she shows no other signs of having a 'damsel in distress' personality, generally able to defend herself even while badly injured.

She can, however, speak to Mordred in her mind, and it was implied she was raised a Druid and that that was how she first met young Mordred and became his childhood sweetheart.

Trivia

 * Nimueh used this name (same pronunciation but different spelling with a "C" instead of a "K") when she infiltrate Camelot in the episode "The Poisoned Chalice".
 * Some fans speculated early on that Mordred and Kara's relationship would be similar to that of Merlin and Freya's in The Lady of the Lake, but the only real likeness between the two are that Freya and Kara were both Druid girls who were kept hidden in Camelot by somebody close to Arthur. Whereas Freya was only a killer because of her curse (and her "crime" was only that she was a Druid), Kara kills willingly for hatred of Arthur and Camelot (her crime was killing several men, whom she claimed were merely casualties of war, and for attempting to stab Arthur after swearing she meant him no harm).
 * Kara's death serves as Mordred's motivation to kill Arthur. As well as motivation to tell Merlin's secret to Morgana.

Gallery
Kara