Géza I (Hungarian pronunciation: [ˈɡeːzɒ]; Hungarian: I. Géza; c. 1040 – 25 April 1077) was King of Hungary from 1074 until his death. He was the eldest son of King Béla I. His baptismal name was Magnus. With German assistance, Géza's cousin Solomon acquired the crown when his father died in 1063, forcing Géza to leave Hungary. Géza returned with Polish reinforcements and signed a treaty with Solomon in early 1064. In the treaty, Géza and his brother Ladislaus acknowledged the rule of Solomon, who granted them their father's former duchy, which encompassed one-third of the Kingdom of Hungary.
Géza closely cooperated with Solomon, but their relationship became tense from 1071. The king invaded the duchy in February 1074 and defeated Géza in a battle. However, Géza was victorious at the decisive battle of Mogyoród on 14 March 1074. He soon acquired the throne, although Solomon maintained his rule in the regions of Moson and Pressburg (present-day Bratislava, Slovakia) for years. Géza initiated peace negotiations with his dethroned cousin in the last months of his life. Géza's sons were children when he died and he was succeeded by his brother Ladislaus.