Diego Gelmírez or Xelmírez (; c. 1069 – c. 1140) was the second bishop (from 1100) and first archbishop (from 1120) of the Catholic Archdiocese of Santiago de Compostela in Galicia, modern Spain. He is a prominent figure in the history of Galicia and an important historiographer of the Iberia of his day. Diego involved himself in many quarrels, ecclesiastical and secular, which were recounted in the , which covered his episcopacy from 1100 to 1139 and serves as a sort of gesta of the bishop's life. He was probably born at Catoira, where his father, Gelmiro or Xelmirio, was the custodian of the castle. He received an education at the court of Alfonso VI, king of León, Galicia and Castile. In 1092, Raymond, count of Galicia, named him his notary and secretary and in 1093 he was the administrator of the Compostelan church. In 1094, Dalmatius was appointed the first bishop of Compostela. Dalmatius died the next year (1095) and the people of the see requested the king nominate Diego administrator again during the vacancy. In 1099, the pope authorised a new episcopal election and Diego was chosen the next year. He was anointed the second bishop of Compostela in 1101. During his tenure, he was given secular rule of the city by Alfonso and he strove to make Compostela a major pilgrimage destination, which he did. He increased the prestige of his see and the volume of pilgrims on the road to Compostela. In 1107 Pedro Fróilaz de Traba, the guardian of the heir, Alfonso Raimúndez, rebelled against Queen Urraca and her new husband, Alfonso the Battler. According to the Historia, he was opposed by a "brotherhood" () led by the knight Arias Pérez and Diego Gelmírez, who had known each other since childhood. Diego Gelmírez had accepted the leadership of the brotherhood late in 1109 or early in 1110. In 1110 a truce between Pedro and the brotherhood was broken when the former took over the south Galician fortress of Castrelo de Miño and installed a garrison there under his wife Urraca and the young Alfonso. Arias promptly besieged it, and Pedro came to defend it. The besieged called on Diego to negotiate terms of surrender, which he did, but the brotherhood had grown suspicious of him and when a deal was struck Arias had Diego, Pedro, and Alfonso all arrested. In exchange for the castles of