Under his leadership, Malaysia became one of the Asian tigers - the group of countries which saw their economies expand rapidly in the 1990s. But he was an authoritarian figure who used controversial security laws to lock up his political opponents.

Most infamously his deputy prime minister, Anwar Ibrahim, was sacked and accused of corruption and sodomy - and later jailed on the latter charge - when he called for economic and political reforms.

Mr Mahathir was also a mentor to Mr Najib, who became prime minister in 2008.

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But Mr Najib has been dogged by corruption allegations. He has been accused of pocketing some $700m from the 1Malaysian Development Berhad, a state investment fund he set up.

He has vehemently denied all allegations and been cleared by Malaysian authorities but the fund is still being investigated by several countries. Mr Najib has been accused of stifling Malaysian investigations by removing key officials from their post.