Alexander Jannaeus is king of Judea from 103 BCE to 76 BCE.

The son of John Hyrcanus, he inherits the throne from his brother Aristobulus I, and appears to have married his brother's widow, Shlomtzion or "Shelomit", also known as Salome Alexandra, according to the Biblical law of Yibbum ("levirate marriage"), although Josephus is inexplicit on that point.

His likely full Hebrew name was "Jonathan"; he may have been the High Priest Jonathan, rather than his great-uncle of the same name, who established the Masada fortress.

Under the name "King Yannai" he appears as a wicked tyrant in the Talmud, reflecting his conflict with the Pharisee party.

He is among the more colorful historical figures, despite being little known outside specialized history.

He and his widow (who became queen regnant after his death) had a substantial impact on the subsequent development of Judaism.

Jannaeus expanded the Hasmonean Kingdom and established the city of Gamla in 81 BC, as the capital for what is now the Golan Heights.