Morganne Lefay

This woman was cunning and severe, she had been recruited to be a member of the holy knights alongside Artorius. Some saw her as wicked and cruel but Artorius saw something else. Unflinching devotion and purpose. Morganne was a woman of few words, her older brother Mordred was the more gifted orator but that meant little to her. For Morganne the world was black and white, right and wrong, and in Artorius she saw the the good that he stood for.
Her arcane talents were the talk of the kingdom, she had a double specialization as an evoker and transmuter. Taking harmless creatures and transforming them into powerful beasts, or blasting holes through stone with lightning bolts. She was a known and feared mage. Artorius was this reputation to his advantage on more than one occasion. Despite this she never placed her self above any other of Artorius' knights. They all served him for their own reasons, only Artorius understood her motivations and she liked it that way. She was not an open or welcoming person but she didn't need to be.
Then Artorius became King of Camhalott and he made her his left hand, trusted advisor and confidante. Many years of peace, until her brother betrayed them all out of obsession. The knights were killed among hordes of undead, the castle was sacked with abyssal monsters, she ran and fought her way through searching for Atorius to rally the defenses. But she found him and Deairmuut in dire circumstances. She found Mordred and his monsters bearing down on them for a final strike, her forthcoming barrage of spells would have made Bixpy or Mordenkainan proud. The moment of pain, confusion, and death allowed her King and fellow Knights to rise and strike fatal blows, Mordred laid smoldering from her fire and acid. She looked down at him in disgust and hate, never blinking as Artorius cursed his name and drove Caliburn the Mage Bane through his chest. The moment his death was absolute she turned away and never spoke of the incident again.
Morganne had always been a survivor by nature but on the tragic day during the Battle of Camlann it might have been possible for her to escape but after so many years with King and fellow knights she knew it would dishonor every moment they had, and so she too went down fighting side by side with the two people closest to her. She died smiling.