Malaysia's general election on Wednesday will be an extraordinary contest, pitting a 92-year-old former authoritarian leader and a jailed reformist he fell out with 20 years ago against a prime minister who has been mired in a multibillion-dollar scandal.

Few doubt that Prime Minister Najib Razak's National Front coalition, which has ruled Malaysia for the six decades since independence, will triumph.

But a robust challenge from the opposition — spearheaded by nonagenarian Mahathir Mohamad, the country's longest-serving prime minister, and his one-time protege Anwar Ibrahim — has produced a hotly contested election.