Story highlights Bal Thackeray founded Shiv Sena, a powerful political party

The movement was founded to defend the Marathi people

He was instrumental in having the name of Bombay changed to Mumbai

Shiv Sena and PM Manmohan Singh appeal for calm

Bal Thackeray, a staunch advocate of Hindu nationalism in India and the leader of a political party that dominated the country's financial capital, died Saturday, his spokesman said.

The 86-year-old Thackeray was a charismatic founder and head of Shiv Sena, the nationalist movement most powerful in the city of Mumbai and the Maharashtra state.

Spokesman Rahul Narvekar said Thackeray died of cardiac arrest and his cremation will be held on Sunday.

Thackeray emerged in the 1960s as a populist leader for the Marathi people, who dominated Mumbai and the Maharashtra state.

Once a newspaper cartoonist, he rose to fame for defending Marathi interests as migrants from other communities streamed into the city, known at the time as Bombay.

The movement has immense political power in Mumbai, India's financial center and site of the legendary Bollywood film industry.

Its symbol is an orange flag, seen planted across Mumbai. Thackeray was instrumental in having the name of Bombay changed to Mumbai, a Marathi name.

And Thackeray had developed a reputation among many Indians as a bit of a godfather, revered by his followers but feared by others.

Over the years, the Shiv Sena movement grew in popularity across India as a Hindu nationalist movement.

Shiv Sena and Prime Minister Manmohan Singh appealed for calm after his death was announced, and authorities have deployed police officers across Mumbai in the wake of his death.

In a series of Twitter messages, Indian Prime Minister Manmohan Singh said Thackeray's leadership helped build Shiv Sena into a "formidable force" in Maharahstra.

"He was a consummate communicator whose stature in the politics of Maharashtra was unique," Singh said. "For him the interests of Maharashtra were particularly important and he always strived to inculcate a sense of pride in its people."