Diego Fernández (fl. 1020 – c. 1046), also known as Diego Fernández de Oviedo, was a member of one of the most noble lineages of the Kingdom of León as the son of Fernando Flaínez and Elvira Peláez, daughter of count Pelayo Rodríguez. He was the second cousin of King Alfonso VI since both shared the same great-grandfather, Count Fernando Bermúdez de Cea. Distinguished with the title of Count at an early age, Diego was the father of Jimena Díaz, wife of Rodrigo Díaz de Vivar El Cid.