Sheala de Tancarville or Síle de Tansarville is one of the main antagonists in game of the video game The Witcher 2: Assassins of Kings.
Along with her colleagues in the Lodge of Sorceresses, she made a conspiracy against kings of the Northern Realms, so they could have own independent country with puppet ruler.
She hired Letho of Gulet to assassinate King Demavend, but after he killed Foltest, she figured out he works for Emperor of Nilfgaard and tried to find him in order to destroy all evidences of her involvement in this regicide.
She protected King Henselt of Keadwen from Letho's colleagues, but Geralt of Rivia eventually discovered she was Letho's client.
She followed the orders of Philippa Eilhart to control her dragon. Depending on player's choices she can die or escape.
If Geralt saves Sheala then he and Yennefer later find her in a prison in Oxenfurt when they are looking for Margarita Laux-Antille who has been captured by King Radovid. Sheala has been extensively tortured beyond the possibility of being saved so either Geralt or Yennefer put her out of her misery in order to spare her from a far more agonizing death.
The Witcher 2: Assassin of Kings
The Witcher 3: Wild Hunt