Olga

Olga was a regent of Kievan Rus' for her son Sviatoslav from 945 until 957. Following her baptism, Olga took the name Elenа. She is known for her subjugation of the Drevlians, a tribe that had killed her husband Igor. Even though it was her grandson Vladimir who adopted Christianity and made it the state religion, she was the first ruler to be baptized.