Olga of Kiev

Olga (Church Slavonic: Ольга; Old Norse: Helga; c. 890–925 – 11 July 969) 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 Rurikid ruler to be baptized.

Olga is venerated as a saint in the Eastern Orthodox Church with the epithet "Equal to the Apostles". Her feast day is 11 July.

Source: Wikipedia — https://en.wikipedia.org/wiki/Olga_of_Kiev