At the age of 92 Malaysia's former strongman leader Mahathir Mohamad became the world's oldest prime minister after a stunning election victory against scandal-haunted leader Najib Razak.

In a win that overturns decades of dominance by the country's main coalition, Mahathir has secured an unlikely second act in the twilight of his political career.

A former doctor who entered politics in 1964, Mahathir governed Malaysia with an iron fist for 22 years, with accusations of rights abuses overshadowing a period that also saw Malaysia transform from a sleepy Southeast Asian backwater into a relatively affluent country.

His return to frontline politics started when he fell out with his one-time protege Najib over allegations huge sums were looted from sovereign wealth fund 1MDB.

In a volte-face that would have been unthinkable just a few years ago Mahathir teamed up with parties that he suppressed while in power to take on the party he once led.

He is remembered fondly by some as a champion of country's Muslim Malay majority and the father of modern Malaysia, credited with policies that helped the economy blossom.

But he was also criticised for disregarding human rights, undermining the judiciary, jailing political opponents and pushing policies that exacerbated racial divisions in the multi-ethnic country.

He was notorious for his acid-tongued attacks on his foes and what he saw as Western neo-colonialism -- in one outburst, he described Europeans as greedy, warmongering sexual deviants.

Mahathir was spurred out of retirement over allegations huge sums were looted from 1MDB, which Najib set up. Najib and 1MDB deny any wrongdoing.

"The biggest mistake that I have made in my life is choosing Najib," he said in one broadside.

"I want to fix this mistake."

The most remarkable aspect of Mahathir's political comeback has been his reconciliation with former nemesis Anwar Ibrahim. Anwar was Mahathir's heir-apparent until the premier sacked him in 1998 over political differences, and he was subsequently jailed on charges of sodomy and abuse of power.  After being released Anwar led the opposition to its best-ever showing in 2013 elections, but was imprisoned again in 2015 under Najib's government.

Mahathir has vowed to hand power to Anwar once he is released.