John Hyrcanus (; Hebrew: יוחנן הרקנוס, romanized: Yoḥānān Hurqanos; Koine Greek: Ἰωάννης Ὑρκανός, romanized: Iōánnēs Hurkanós) a Jewish high priest and ruler of Judea from the Hasmonean dynasty (born 164 BCE, reigned from 134 BCE until he died in 104 BCE). In rabbinic literature he is often referred to as Yoḥanan Cohen Gadol (יוחנן כהן גדול‎), "John the High Priest". John combined political and religious authority and secured Judea's independence from Seleucid control. His reign consolidated the Hasmonean state, expanded its territorial boundaries, and incorporated neighboring populations, laying the foundation for the policies and territorial expansions of subsequent Hasmonean rulers.
Hyrcanus assumed power following the assassination of his father, Simon Thassi, a brother of Judas Maccabeus, by Ptolemy ben Abubus near Jericho. He escaped the attack that killed his father and some of his brothers and was accepted as high priest in Jerusalem. Initially, he maintained relations with the Seleucid Empire, paying tribute while preserving autonomy and participating in military campaigns under Antiochus VII Sidetes, including operations against the Parthians. However, after Antiochus VII's death in 129 BCE, Hyrcanus ceased tribute payments and acted independently, establishing the de facto sovereignty of Judea.
During his reign, Hyrcanus conducted military campaigns to expand Hasmonean territory, which until then was largely confined to central Judea. He captured the regions of Samaria and Idumaea, destroyed the Samaritan temple at Mount Gerizim, and incorporated the Idumaean population, requiring conversion to Judaism. He also extended Hasmonean control over parts of Transjordan and Galilee. Hyrcanus is the first attested Hasmonean ruler to employ foreign troops, and he may have founded Hyrcania, a fortress in the Judaean Desert that bears his name.
Hyrcanus's policies and territorial expansions laid the foundation for the subsequent reigns of his sons, Aristobulus I and Alexander Jannaeus, who assumed the title of king alongside that of high priest.