Key players in the Pakistani polls include two who cannot hold political office, former premier Nawaz Sharif and the military, as well as the leaders of the three main parties.
Dubbed the Lion of Punjab, he was prime minister thrice but has never completed a term, his latest ending when he was ousted by the Supreme Court last year and banned from politics for life over corruption.
He was sentenced in absentia to 10 years in prison. He returned to Pakistan from London a week later and was arrested.
Analysts said he has returned to fight for his political life, as his Pakistan Muslim League-Nawaz (PML-N) party stumbles in the campaign. His dispute with the army is largely attributed to his desire to shift power to the civilian government and to seek warmer ties with arch rival India.
The army, perceived as the country's strongest institution, has ruled Pakistan for roughly half of its nearly 71-year history and is widely believed to control foreign and defence policy.
It has been broadly accused of what one think-tank called a "silent coup" against the PML-N and in favour of opposition stalwart Imran Khan.
Several cases of kidnappings and threats against media and political activists have been reported, and diplomats have voiced concern over censorship allegations ahead of the polls.
The army has denied the claims and said it takes "no direct role" in the election.
former World Cup cricket hero turned politician, he has made no secret of his ambition to become prime minister.
Known in the West mainly as a talented sportsman and an infamous playboy, he presents a significantly more conservative and devout face to Muslim Pakistan.
Critics consider him unfit for office. His Pakistan Tehreek-e-Insaf (PTI) party, founded in 1996, has long had to settle for a handful of seats nationally.
Some call him "Taleban Khan" and attack his repeated calls for talks with violent insurgent groups. He has also been criticised for pandering to Islamist hardliners. Others suspect him of links to the army.
Nawaz's younger and less charismatic brother Shahbaz became president of the PML-N after his elder sibling was ousted and is leading the party into the vote.
His quieter style is being overshadowed by his brother's loud quarrel with the military. But he occupies a key position in politics, having spent more than 10 years as chief minister of Punjab province, which represents more than half the country's population of 207 million.
Mr Shahbaz, also an influential businessman, is reputedly less stubborn and therefore more acceptable to the military than Nawaz or his anointed political heir and daughter Maryam, who has also been jailed for corruption.
BILAWAL BHUTTO ZARDARI
His mother Benazir Bhutto, the first woman to lead a Muslim-majority country, was assassinated in 2007. His grandfather Zulfikar Ali Bhutto, also a prime minister of Pakistan, was hanged in 1979.
The 29-year-old has little experience and the chance of election victory for his family's Pakistan People's Party is deemed almost nil - though he could become kingmaker by joining forces with the PML-N or PTI, if either failed to win an outright majority.
The task would be difficult for the scion of a family who once dominated Pakistani politics but whose party is now in decline, even challenged in its stronghold in Sindh province.