Answer
Olga of Kiev was a regent of Kievan Rus from 945 until her death in 969. She was the widow of Igor of Kiev, who was murdered by the Drevlians in 945. Olga avenged his death by burning the Drevlians alive in their wooden fort. She then ruled Kievan Rus for 24 years, during which time she strengthened the city's defenses and promoted Christianity.