Géza I (I. Géza) (c. 1040 – 25 April 1077), King of Hungary (1074-1077). During King Solomon's rule he governed, as Duke, one third of the Kingdom of Hungary. Afterwards, Géza rebelled against his cousin's reign and his followers proclaimed him king. However, he never achieved to strengthen his position, because King Solomon could maintain his rule over the Western part of the kingdom.
Géza was probably his pagan name, because he was baptized Magnus. In 1048, the family moved to Hungary, where his father received as appanage one third of Hungary ("Tercia pars Regni") from his brother, King Andrew I of Hungary who had acquired the throne from King Peter after a pagan revolt. Following his accession, King Andrew I had to face the attacks of Henry III, Holy Roman Emperor whose supremacy had been acknowledged by King Peter. King Andrew I and Duke Béla cooperated closely against the German attacks and they could preserve Hungary's independence. However, they cooperation began to loosen from 1053 when the king fathered a son, Solomon, because from that time he wanted to ensure his son's inheritance against his brother, who pursuant to the old Hungarian costums, as the oldest member of the royal family, could lay claim to the throne in case of the king's death.
In 1057, King Andrew I had Solomon crowned to ensure his accession, and Géza had to participate in the coronation together with his father and his brothers, Ladislaus and Lampert. However, Duke Béla and his sons left the country in 1059 and they returned with Polish troops in the next year. King Andrew I lost two battles against his brother and died, and after his death Béla was crowned on 6 December 1060.
During his father's reign, Géza was his main adviser and after his father's fatal accident it was he who administered the defence of the country against the German troops which entered Hungary in order to ensure Solomon's rule who had escaped to Germany in 1060. After his father's death on 11 September 1063, Géza offered to accept's his cousin's rule if he received his father's former duchy. However, King Solomon refused the offer and the superiority of his troops obliged Géza and his brothers to leave Hungary and they went to Poland. However, after the withdrawal of the German army, they came back to Hungary followed by troops King Bolesław II of Poland, their maternal cousin, provided them.
The parties, however, wanted to avoid the civil war and therefore they accepted the mediation services of the bishops, and they made an agreement on 20 January 1064 in Győr. Under the agreement Géza and his brothers accepted Solomon's rule, and they received their father's former duchy, i.e., the one third of Hungary.
In the next years, Géza and his brothers collaborated successfully with the king. In 1067, they led an army together to provide assistance to Géza's brother-in-law, King Dmitar Zvonimir of Croatia against Venice. In 1068, when the Pechenegs had overrun the territories of Transylvania, Géza, his brothers and the king went together against them and they won a victory at Kerlés. In 1071, King Solomon and the dukes led a campaign against the Byzantine Empire and laid siege to the fortress of Belgrade. The siege lasted two months, and the Greek commander surrendered the fort to Géza not to the king. Moreover, Géza denied to hand over the king's share of the booty and set the Greek captives free without the king's permission.
Having the Byzantine troops reoccupied Belgrade in the next year, Géza and King Solomon led their armies together against the Greeks, but Géza left his two brothers behind, because he was worrying about that the king's partisans would try to occupy their duchy during their absence. The campaign was a total failure, because the king and the duke were not able to cooperate during the siege any more.
During 1073, both King Solomon and his cousins were preparing for the coming struggle. The king sent his envoys to his brother-in-law, King Henry IV of Germany, while Géza and his brothers were seeking the help of their Polish and Czech relatives. In the beginning of 1074, before the Polish and Czech troops arrived, King Solomon led his armies against the dukes' territory and defeated Géza's troops on 26 February at Kemej. However, after the arrival of the reinforcement from Poland and Bohemia, the dukes' armies started a counter-attack and they won a decisive victory over King Solomon's troops on 14 March in the Battle of Mogyoród.
Géza tried to obtain the international acknowledgement of his rule; therefore he sent embassies to Pope Gregory VII, who was struggling against the German king, and to Michael VII, Emperor of the Byzantine Empire. The pope claimed the recognition of his supremacy over Hungary which Géza did not accept, but the Byzantine emperor sent a crown, that was later incorporated with the ancient crown of Hungary, to him and Géza was crowned by that crown because the ancient crown was in the possession of King Solomon. At this time, Géza married a niece of Michael VII's military commander Nikephoros Botaneiates. During his reign Géza set up the Abbey of Garamszentbenedek and finished the building of the cathedral of Vác. In 1076, he sent his troops led by his brother, Duke Ladislaus against Pozsony, but King Solomon could beat off the troops. After this failure, according to the chronicles, Géza, who had become more and more ill, was thinking of his abdication in favour of his opponent, but they did not reach an agreement.
He was buried in the cathedral of Vác.