Nicholas Kratzer (1487?–1550) was a German mathematician, astronomer and horologist. Much of Kratzer's professional life was spent in England where he was appointed astronomer to King Henry VIII. Born in Munich, Kratzer came to England in 1516 and established himself as part of the artistic and scientific circle around Sir Thomas More. Kratzer tutored More's children in mathematics and astronomy and More introduced him at court in much the same way as he had their mutual friend Hans Holbein the Younger, who painted this portrait.