The impetuous younger son of Alexander Jannai and Salome Alexandra rebelled against his mother, defeated his older brother Hyrcanus at Jericho and proclaimed himself high priest and king. He was supported by the Sadducees but was driven from Jerusalem [65 BCE] by Arab armies of Nabatea [Jordan], who came to his brother's aid at the invitation of Antipater. Aristobulus called for and received support from the Roman legate of Syria. But Hyrcanus appealed directly to Pompey, the Roman conqueror of Syria, who was in Damascus.
Aristobulus sent a counter-petition to Pompey. Yet, rather than wait for Pompey's decision — which was complicated by an appeal by residents of Jerusalem to abolish the Judean monarchy and return to a theocracy — Aristobulus seized the fortress of Alexandrium. Pompey used this as a pretext to attack Jerusalem. When Aristobulus' aristocratic supporters fortified themselves in the temple, Pompey breached the walls, slaughtered thousands of Jews in the sanctuary and even entered the holy of holies. Aristobulus was sent to Rome as a hostage. He was eventually released by Julius Caesar [49 BCE], only to be poisoned by Pompey's supporters before he could wrest control of Jerusalem from supporters of his older brother.
Sources: Into His Own