The Ancient One's history is presumably similar to his Earth-616 counterpart's. He was a teacher at the mystic monastery of Kamar-Taj.
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History
One day, Stanley Stewart came to him to teach him how to control his powers. The Ancient One told Stewart that his powers were given to him by the Vishanti, and to get control of his powers, he need to learn how to stare a flower, which would help him focus his mind. Stewart eventually learned how to focus and stare at the flower after 17 days of trying.