Olga is the East Slavic form of the Old Norse Helga ("holy, blessed"). Saint Olga of Kiev (c. 890-969) was the regent of Kievan Rus' (945-963) and the first Christian ruler of what would become Russia — baptized in Constantinople in 957, she set the stage for her grandson Vladimir's mass conversion of Rus' in 988.
Subject of icons throughout Eastern Orthodox Christianity.
Olga does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Olga reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.