Seondeok (선덕여왕, 595-647) was the 27th ruler of Silla — the first reigning queen of any of Korea's Three Kingdoms. She built Cheomseongdae, the oldest surviving astronomical observatory in East Asia, and oversaw the founding of the great Buddhist Hwangnyongsa Temple. Famous for solving riddles and predicting the future — including the time and place of her own death.
Subject of the popular Korean historical drama Queen Seondeok (2009).
Seondeok 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 Seondeok reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.