He was never elected to office but was seen for decades as Mumbai's most powerful man. He created an army of supporters by weaving Hindu fundamentalism with ardent defense of Marathis, Mumbai's dominant ethnic group.
Thackeray founded his political party, the Shiv Sena — which means Shiva's Army — with the sole aim of keeping people who are not from Maharashtra out of the state and stemming the spread of Islam and Western values.
Spurred by Thackeray's rabble-rousing speeches, his supporters routinely resorted to violence against Muslims and migrant workers who had come to Mumbai in search of work. He is among those blamed for a wave of religious violence in 1992 that left nearly 1,000 people dead in Mumbai alone.
Analysts say it was as sense of fear that kept millions of people off the streets of the bustling city on Sunday. Nearly 20,000 policemen patrolled the deserted streets, mainly because of the violent history of the Shiv Sena.
No violence occurred Sunday. A day later, a relieved Mumbai police chief, Satyapal Singh, praised the "unexpectedly orderly behavior" of Thackeray's supporters.
But the thuggish behavior was in evidence Monday when a mob of Thackeray's supporters stormed the orthopedic clinic, destroying its operating rooms and much of its equipment. Nurses and patients fled but no one was hurt.
On Tuesday, police said they had detained nine men for their involvement in the attack of the clinic. It was not immediately clear if the men belonged to the Shiv Sena.
The Mumbai arrests came barely two months after the Maharashtra police arrested a political cartoonist on sedition charges for drawings that mocked corruption in the Indian government. The charges were dropped and the cartoonist is out on bail. Earlier this year, a university professor was arrested in the state of West Bengal for forwarding an email cartoon that caricatured the chief minister there.