Lady Sariel is a powerful PC turned NPC spanning several campaigns.
Sariel became a fervent foe to Saint Ajax the Invincible when her father, the elven king of the Orchid Court, swore fealty to Ajax. During a battle with the Scion of Orcus, she was killed and turned into a vampire spawn. When the Scion was killed, she regained her free will and became Lady Sariel the Vampire Queen.
Seeking the Teeth
Lady Sariel decided to begin collecting the Teeth of the Dragon, believing that by collecting all of them, she could "raise the Dragon" and use its power to destroy Ajax. Upon realizing that Nekodemus possessed Arcturus, she began sending minions after him to retrieve the Sword of Stars, but his ability to teleport the sword back to his hand continually thwarted her attempts. She did, however, succeed in locating and obtaining Orion, the Master Sword. She also gained control of the Oracle during this period.
Disguising herself as Sir John, a minstrel of the Baron of Tor, she secured an invitation into Castle Rend. Once inside, she revealed herself to Nekodemus and demanded that he hand over Arcturus and Scorpius so that she could raise the Dragon and destroy Ajax. Upon learning that Sariel had attained Orion, Nekodemus attempted to attack Sariel with his enchanted greataxe Wound. The attack, which should have been devastating, was ineffectual as Wound refused to harm the wielder of the Master Sword. Sariel had one of her retainers, a death knight, bring in a captured Lord Saxton as a prisoner, offering him in exchange for the swords. As proof of her power, she summoned Bhaltair from the ground, now a vampire spawn under her control. The residents of Castle Rend finally accepted her bargain and handed Arcturus and Scorpius over to Lady Sariel.
The Final Contract
In what appears to have been her final confrontation with Ajax, Lady Sariel struck at him with the sword named Orion. Ajax countered her attack with the Jade Hand and in doing so destroyed Orion. The ensuing blast disintegrated Lady Sariel. Her current fate remains unknown.
Behind the Scenes
Sariel was a player character in one of Matt's previous campaigns, played by his friend Jess. After Sariel was killed and made undead while fighting the Scion of Orcus, Matt reused her as an antagonist and ally of the player characters in future campaigns.