J. Edgar Hoover

Assassin has been shown largely to be manipulative and conniving, aiming to control the actions of the other Servants into destroying themselves, however her plots are often foiled to comedic effect, such as Gudako bursting in on her for badmouthing Paul Bunyan. She is also indicated to be extremely proud and boastful, even by her own admission, believing that surviving the War to the end is the only way the Servants can get implemented into Fate/Grand Order. Despite her pride, she is shown to have a weakness in her Mother's approval.

She considers her Master as a Maternal figure, trying to dissuade her efforts to expose what Assassin knew by claiming that she was her "Mama" rather than her "Mother", but failing and exposing the location of Gudako upon Olga expressing disappointment, claiming she would not expect anything from her anymore.

(Source: TYPE-MOON Wiki)