What happened
Olmert faced several overlapping investigations by the time he resigned in 2008, including allegations he had received cash-stuffed envelopes from an American businessman over more than a decade spanning his time as mayor of Jerusalem, trade minister, and prime minister, and a separate case (the Holyland affair) involving bribes taken over a major Jerusalem real-estate development. He resigned as party leader in September 2008 once it became clear the corruption allegations made his position untenable, though he remained caretaker prime minister for several more months until Netanyahu formed a government after the 2009 election.
His subsequent legal path was unusually prolonged: he was acquitted on the original envelopes charge at trial but convicted in 2014 on a related bribery charge (the Holyland case) and separately convicted in 2015 on an obstruction of justice charge for attempting to influence witness testimony. Israel's Supreme Court reduced his original 6-year sentence to 18 months on appeal; he ultimately served 16 months, becoming the first former Israeli prime minister to serve time in prison for a criminal conviction. Olmert has maintained his innocence on the core bribery allegations even after the convictions were upheld on appeal.