Queen of Years was a title given to a chosen female in the Sun-singers of Akhet. The Queen of Years knew all the songs, melodies, rhythms and poems ever written or sung by that culture. She was required to sing to the Mummy, in front of thousands of the natives and residents of the system, in a big millennial event called the Festival of Offerings. After singing, she would be sacrificed. Every time a Queen of Years died, a new one replaced her.
During the time when the Eleventh Doctor and Clara Oswald visited Akhaten, a young girl called Merry Gejelh held the title. She was chosen and taken from her family as a baby, after the last Queen of Years died. Clara fed the leaf that had provoked the meeting of her parents to Akhaten and the potential variables in causality it provided proved too much for the "god" whose destruction saved Gejelh from sacrifice. (TV: The Rings of Akhaten)