Concerns escalated in 2014 as 1MDB slid into an $11-billion debt hole, and intensifying public scrutiny revealed missing funds.
The scandal first came to light through the Sarawak Report news portal and gained further traction in 2015 when The Wall Street Journal published documents showing Najib received at least $681 million in payments to his personal bank accounts.
The US Justice Department launched its own probe after claims that stolen Malaysian public money was laundered through the US financial system, and has filed lawsuits seeking some $1.8 billion in assets allegedly purchased with the cash.
The department said more than $4.5 billion was stolen from 1MDB between 2009 and 2015 by high-level officials at the fund and their associates.
Tens of millions of dollars were used in 2012 by Najib's stepson Riza Aziz, an aspiring film producer, to fund the Hollywood film "The Wolf of Wall Street", starring Leonardo DiCaprio.
Hundreds of millions were also used, mainly by Riza and Low, to purchase high-end real estate in Beverly Hills, New York and London.
A Monet painting bought for $35 million, a Van Gogh for $5.5 million, a $35-million Bombardier jet, a $100-million stake in EMI Music Publishing, and a $250 million yacht were also ticked off the shopping list.
Najib desperately sought to contain the scandal, targeting critics and introducing repressive laws, but the allegations hit the popularity of his long-ruling coalition and contributed to a shock election defeat in 2018.