He formed the Shiv Sena in 1966 as a "sons of the soil" movement, to fight for the rights of native Maharashtrians who, he believed, were under threat from other ethnic migrants.
Referred to as the 'Tiger' by his supporters, the cartoonist turned politician has courted controversy ever since he founded the hardline Hindu Shiv Sena party more than 30 years ago.
He attracted particular opprobrium after the 1992-3 communal riots, which he was alleged to have incited.
The Shiv Sena has acquired a reputation of promoting religious and ethnic chauvinism while targetting minorities, especially Muslims.
Last October, it was trounced by the Congress party in elections to the Maharashtra assembly, after ruling the state for nearly five years.
'Sons of the soil'
Bal Thackeray, who is 73, began his career as a political cartoonist in a Bombay newspaper in the 1950s.
He formed the Shiv Sena in 1966 as a "sons of the soil" movement, to fight for the rights of native Maharashtrians who, he believed, were under threat from other ethnic migrants.
The party ran an intimidating and often violent campaign, targetting south Indians who worked as clerks or owned small restaurants in Bombay.
In later years, the Gujarati and the Muslim communities were similarly targetted.
Mr Thackeray commands an almost fanatical following among his party members.
Although he has never stood for election, he wields power over Bombay through a tightly controlled network of party cells, which can be activated at his command.
Attacks
In the past few years, Mr Thackeray's fiery speeches and pronouncements have frequently embarrassed the BJP-led government in Delhi, which includes the Shiv Sena.
Last year, party activists vandalised a cricket pitch in Delhi, in protest against a tour by the Pakistan national team.
The Shiv Sena also targetted a legendary Muslim Bollywood star, Dilip Kumar, who had been presented Pakistan's highest civilian award.
Mr Thackeray's current troubles stem from the inflammatory editorials published in his party newspaper, Saamna (Confrontation) in 1992.
His remarks followed the illegal demolition of the 16th century Babri mosque in the northern town of Ayodhya by Hindu militants.
A judicial committee, which investigated the ensuing communal riots, accused Mr Thackeray of sparking anti-Muslim violence in Bombay, which led to more than 1,000 deaths.