Ansur, Assur, or Asur Fernández (died 947/50) was a powerful Castilian nobleman and military leader in the Kingdom of León during the reign of Ramiro II. He was the first Count of Monzón, probably from before 939, certainly by 943, and he was Count of Castile in 943–45 in opposition to the deposed Fernán González. His family was known as the Banu Ansúrez (Assuriz).