A monk known for his incendiary anti-Muslim rhetoric leads the Hindu nationalist Bharatiya Janata Party into elections in India's most populous state Thursday, where a strong win could put him in pole position to succeed Prime Minister Narendra Modi.

Yogi Adityanath, 49, has stirred controversy since his surprise appointment in 2017 as chief minister of Uttar Pradesh, a state in northern India home to over 200 million people -- more than the entire population of Brazil.

Office has done nothing to temper his views, and as he seeks a second term he is exhorting Hindu voters to back the BJP while riding roughshod over Muslims who make up one-fifth of the state's population.

A hardline protege of Modi, Adityanath has soared in popularity beyond Uttar Pradesh, thanks to his fiery speeches and projection as a tough, no-nonsense administrator.

"He is brazenly open about his Hindu politics and ideology... He has projected himself as a Hindu leader and that's what brings him crowds and votes," said journalist and political commentator Sunita Aron.

"When he does Muslim-bashing, he grabs eyeballs and audiences," she told AFP.

In the run-up to the bellwether polls this week, the saffron-clad monk did not mince his words, saying it would be a fight between "80 per cent and 20 per cent", referring to the state's demographic split on religion.

Crowds thronged one rally for a glimpse of the ascetic, despite coronavirus restrictions, cheering loudly each time he made a mocking reference to Muslim voters.

"They are worshippers of Jinnah," he tweeted last month, referring to Mohammad Ali Jinnah, the founder of India's arch-rival neighbour Pakistan.

"Pakistan is dear to them, we sacrifice our life for Maa Bharati (Mother India)."

Sacred cow

Born Ajay Singh Bisht, Adityanath comes from a humble background -- his father was a forest ranger and he was one of seven siblings.

While studying mathematics at university, Adityanath became an activist in the student wing of the Rashtriya Swayamsevak Sangh, a right-wing Hindu organisation considered the ideological fountainhead of the BJP.

After graduating, he became a priest of Gorakhnath Temple, known for its strong Hindu supremacist tradition, and at the same time went into politics, elected to parliament for the first time in 1998 aged just 26.

Along the way, he founded a vigilante youth army named Hindu Yuva Vahini.

Volunteers of the group regularly rough up Muslims accused of slaughtering cows or "love jihad" -- a term used by nationalist extremists to accuse Muslim men of seducing Hindu women in order to force them to convert.

Cows are considered sacred by Hindus and their slaughter is banned in many states, including Uttar Pradesh.

Adityanath himself has several criminal cases pending against him in various courts.

In 2007, he spent 11 days in jail for trying to foment communal tension. In one speech he vowed: "If they (Muslims) kill one Hindu man, then we will kill 100 Muslim men."

But his notoriety did nothing to impede his twin-track progress: in 2014, he was appointed head priest of his temple.

After taking the reins as chief minister three years later, Adityanath announced curbs on slaughterhouses and on the use of loudspeakers for the Muslim call to prayer, fuelling an atmosphere of fear and intimidation.

Indian media reports say more than 100 alleged criminals -- most of them Muslims or low-caste Dalits -- have been extra-judicially killed by Uttar Pradesh police under his administration, a charge Adityanath denies.

Heir apparent?

His political style aligns firmly with his party, which has been accused of fuelling religious intolerance for electoral gain, calling into question India's long-cherished secular and democratic credentials.

Adityanath also appears to be a complementary foil to Modi, driving the party's Hindu majoritarian agenda with ferocity while the prime minister is to some extent constrained by the obligations of his office.

Within the party, he is seen as a possible successor to Modi, who is 20 years his senior.

A strong showing in the election -- which extends over seven rounds of voting before counting in early March -- will bolster that status.

Opinion polls put the BJP at around 43 percent, well ahead of the socialist Samajwadi party and easily enough for an absolute majority.

"It's too early to say about his role in the future. But it's clear that he is second only to Modi," a BJP member told AFP, requesting anonymity.

"It may be a bit premature but of course he is a contender for the prime minister's job."