Fortún Garcés Cajal (died 1146) was a Navarro-Aragonese nobleman and statesman, perhaps "the greatest noble of Alfonso the Battler's reign". He was very wealthy in both land and money, and could raise two to three hundred knights for his retinue, funded both out of his treasury and enfeoffed on his lands.
In 1113 Fortún replaced Diego López I de Haro in the large and important tenancy of Nájera and Viguera. He held it until 1135. After the death of Alfonso the Battler in 1134, Fortún became a vassal of King Alfonso VII of Castile.
Nothing is known of Fortún's life before he appears at the court of Alfonso the Battler in 1110. In that year he witnessed Alfonso's arbitration of a dispute between the diocese of Pamplona and the abbey of Saint-Sernin at Toulouse over possession of the church of Artajona. Thereafter, Fortún's rise was rapid. As a servant of the crown, Fortún held several lordships (tenencias), compact territorial fiefs where a nobleman governed on behalf of the crown. These were not hereditary lordships, but were granted by the king, the lords (tenentes) holding them as long as the king wished. In 1113, Fortún replaced Diego López I de Haro in the large and important lordship of Nájera and Viguera. This territory was in the Kingdom of Castile, on the border with Aragon, and Fortún was able to hold it only because of Alfonso the Battler's marriage to Queen Urraca of Castile in 1109. Although the marriage was annulled in 1112, Alfonso had a base of support in the Castilian kingdom and substantial influence in the contested border region that had once belonged to Navarre. Fortún managed to hold onto Nájera until after Alfonso's death in 1134, when he accepted the overlordship of King Alfonso VII of Castile, who had succeeded his mother in 1126. The last record of Fortún's tenancy comes from 1135, and sometime before 1139 he had been replaced by his predecessor's son, Count Lope Díaz de Haro.