Andrew I (born c. 1016, died c. 1061), was King of Hungary 1047-61.

He was from a younger branch of the Árpád dynasty, and born as son of Vazul, former lord of Gran and regions much corresponding today Slovakia. Hungarian tribal society was not in favor of primogeniture, but of agnatic seniority as order of succession, which made other males of the Arpad dynasty, cadet lines, dangerous to the incumbent king. Andrew's branch of the dynasty had long been rivals to the elder branch, which Stephen I of Hungary and his father belonged to. For the recent half a century, the rivalry had centered much on conflict between paganism and christianism, represented (and utilized), respectively, by the younger and elder branch. The elder branch went extinct in male line in 1038, which opened new opportunities to the younger, surviving male line; because Hungarian clannish society yet believed in inheritance through male line. Stephen's female-line successors Aba Samuel and Peter Urseolo felt necessary to suppress the rival family. Andrew's mother was probably the woman who reportedly was a daughter of the Tsar of Bulgaria.

A period of dynastic struggle following the death of Stephan I in 1038 was concluded after the death of Peter Urseolo, as Andrew I took the Hungarian throne for his branch of the Árpad dynasty.

Under Sámuel Abas rule Andrew and his brothers Levente and Béla had been exiled from Hungary, fearing for their lives. First having fled to Bohemia, they continued to Poland where Béla married into that royal family. Andrew and Levente, possibly feeling overshadowed by their brother, continued on, settling in Kiev and Andrew married Anastasia, a daughter of Grand Duke Yaroslav the Great.

Their return to Hungary in 1046 sparked the Vatha pagan rising, where Andrew through pagan support managed to wrest the crown from Peter Urseolo. Andrew was crowned in 1047 and had strengthened his rule by military success, in part thanks to pagan support. Nevertheless, he continued the policies of christianization that had previously been in place. As a Hungarian king Andrew still remained allies with his former hosts in exile, the Kievan Rus'.

The relation to the Holy Roman Empire remained tense. The previous king, Peter Urseolo, had been a close ally of Emperor Henry III, and during his latter reign, Hungary had been part of the Holy Roman Empire. Henry now undertook two largely unsuccessful campaigns against Hungary, in 1051 and again in 1052. Andrew then formed an alliance in 1053 with Conrad II, Duke of Bavaria, supporting thus the opposition against the emperor.

In 1057 Andrew tried to ensure his succession, by having his five-year-old son Solomon crowned as king. This proved unsuccessful, as several years later Andrew's brother Béla I managed to unseat Andrew and gain the throne, if only for a short time.

Andrew and his family are buried in the Tihany abbey, founded by him on the shores of Lake Balaton.

His son never properly managed to establish himself as king; the younger line, that of Bela's, winning gradually, particularly because Solomon did not leave surviving male descent. Andrew's daughter married a duke of the Czech, however descent continuing only through her daughter, who married Wladyslaw I, Duke of Poland and became mother of Boleslaw III, Duke of Poland (1085-1138) (great-grandson of Andrew). Thus, Andrew's line continues in the Piast dynasty and not in Hungary.

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