Mayor of Castile, originally called Muniadona (or Muñadona), she is variously called Munia (or Muña) Mayor (or just Munia or Muña). In Spanish, she is called Muniadona de Castilla. It is said that her husband, Sancho the Great, king of Navarre, renamed her from her contemporary name Muniadona to Mayor, for she was the eldest in her family. She was the countess of Castile from 1029 to 1032, when she died. She was the daughter of Count Sancho I of Castile. Through her marriage to Sancho she was the Queen consort of Navarre.

In 1029, the Count García II of Castile, Mayor's brother, was assassinated by the Vela family of León. This meant that Mayor's husband, Sancho the Great, inherited the countship as his brother-in-law.

Mayor was the mother of four sons:
• Ferdinand the Great, king of Castile and León
• García, king of Navarre
• Gonzalo, king of Sobrarbe and Ribagorza
• Bernardo