Get to know the main players

Here is a look at the election's main players:

Nawaz Sharif

Nawaz Sharif, dubbed the Lion of Punjab, was thrice prime minister but never completed a term. His latest stint ended last year when he was ousted by the Supreme Court over corruption, and later banned from politics for life.

His woes reached their peak earlier this month when he was sentenced in absentia to 10 years in prison. Sharif spectacularly returned to Pakistan from London a week later and was arrested.

Analysts say he has returned to fight for his political life to boost his Pakistan Muslim League-Nawaz (PML-N) party's stumbling campaign.

Seen as a combative and tenacious figure, Sharif claims he is being targeted by the military -- with which he was once close.

The dispute is largely attributed to his desires to shift power to the civilian government and seek warmer diplomatic relations with arch-rival India.

The military

The army, considered the country's strongest institution, has ruled Pakistan for roughly half its nearly 71-year history, and is widely believed to control foreign and defence policy.

It has been broadly accused by the media, analysts, activists and politicians 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, threats and pressure against the media and political activists have been reported, and diplomats have voiced concern over censorship allegations ahead of the polls.

The army denies the claims, saying it has "no direct role" in the election.

Imran Khan

A cricket hero-turned-politician, Khan has become the main opposition leader in recent years and makes no secret of his ambition to become prime minister.

Known mainly in the West as a talented sportsman and infamous playboy, he presents a significantly more conservative and devout face to Muslim-majority Pakistan.

His Pakistan Tehreek-e-Insaf (PTI) party, founded in 1996, governed northwestern Khyber-Pakhtunkhwa province for five years but had to settle for a handful of seats nationally after the 2013 election.

The fall of Sharif and the PML-N's floundering campaign represents Khan's best chance yet to become prime minister, even if an outright majority remains uncertain.

Critics consider him unfit for office. Some call him "Taliban Khan" because of his repeated calls for talks with violent insurgent groups. He has also been criticised for pandering to Islamist hardliners over blasphemy.

Others openly accuse him of having links to the army.

Shahbaz Sharif

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's campaign.

His quieter style has been overshadowed by Nawaz's loud quarrel with the military. But he occupies a key position in Pakistani politics, having spent more than 10 years as chief minister of Punjab, home to more than half of the country's population of 207 million.

Shahbaz, also an influential businessman, is reputedly less stubborn when it comes to the military, and therefore more acceptable to the generals than Nawaz.

There has long been speculation that the two brothers have clashed over their political differences, but they have never corroborated the claims.

Bilawal Bhutto-Zardari

Bilawal Bhutto-Zardari is the son of the charismatic Benazir Bhutto, who was twice elected prime minister and assassinated in 2007. His grandfather Zulfikar Ali Bhutto, also a prime minister, was ousted in a coup and executed in 1979.

At 29, Bhutto-Zardari has little experience and the chance of election victory for his family's Pakistan Peoples Party is deemed almost nil -- though he could become kingmaker in a coalition if the PML-N or the PTI fail to win an outright majority.

The PPP once dominated Pakistani politics but is now in decline, facing a strong challenge even in its strongholds in southern Sindh province.

Bilawal's father Asif Ali Zardari, nicknamed "Mr 10 percent" by many in Pakistan because of numerous accusations of corruption, has previously been president of Pakistan.

There is speculation Asif, believed to be the main decision-maker in the PPP, could seek the post again -- or demand other concessions -- in any coalition deal.