In a comprehensive article in the April-June 2002 issue of The Marxist, Ashok Dhawale wrote: 

As is only too well-known, it was the ruling Congress party that nurtured and supported the SS [Shiv Sena] for over two decades from the mid-sixties to the mid-eighties. In the early phase, this support was given to break the Communist hold over the trade union movement in Mumbai; in the later phase, it was to settle factional scores within the Congress itself. At the same time, it is also true that, with the sole exception of the Communists, all other opposition parties in the state have also collaborated with the SS at various times, their leaders sharing the platform with the SS supremo and some of them even going to the extent of striking electoral alliances with the SS in local elections.

The SS has always been under the authoritarian grip of its demagogic supremo Bal Thackeray, who has never disguised his contempt for democracy and adulation of dictatorship. His servile support to the Emergency, although couched in these ideological terms, actually had the much more banal motive of somehow staying out of jail, an experience that he is known to dread. Thackeray has publicly glorified the likes of Adolf Hitler and Nathuram Godse, and this has given immense vicarious pleasure to the dominant hardcore elements of the Sangh Parivar...

This first rally of the SS ended in a manner that accurately foretold the shape of things to coma. After inflammatory speeches by Thackeray and others, the dispersing mob savagely attacked shops and restaurants owned by South Indians, looted them and set them on fire. And as was to happen on innumerable later occasions, the police did not lift a finger against these hoodlums! This was obviously under special instructions from Congress chief minister Vasantrao Naik and home minister Balasaheb Desai, from both of whom Bal Thackeray and his hordes were to enjoy full protection for the next ten years! Twenty years later, in the mid-eighties, it was another Congress chief minister of the same name, Vasantdada Patil, who was to take the moribund Shiv Sena under his wing, help it to regain control over the Mumbai municipal corporation, and enable it to spread its communal tentacles all over Maharashtra...

The SS inaugurated its new communal drive with the ghastly communal riots in Bhiwandi, Kalyan, Thane and Mumbai that were unleashed in May 1984. The provocation for the riots was a public speech by Thackeray wherein he made derogatory remarks against the Prophet, Mohammed Paigambar. These remarks were printed in exaggerated form by some Urdu papers. As a reaction to this, in far-off Parbhani in the Marathwada region, a Congress MLA, A.R. Khan organised a large protest action in which Thackeray's photo was garlanded with shoes. This ignited the fuse which led the SS to unleash massive riots in which at least 258 people were killed, thousands injured and property worth crores destroyed. The riots were replete with terrible instances of cruelty, the most heinous being the Ansari Baug massacre at Bhiwandi.

It has been clearly established that the main culprit in these riots was the SS, aided by various RSS outfits on the one hand and by the Jamaat-e-Islami on the other. The other major culprit was the Congress(I) state government which was then headed by Vasantdada Patil. While the build-up to these riots, consisting of rabid communal propaganda and even collection of weapons, was going on openly for two months in Mumbai and Bhiwandi, the government did absolutely nothing. The attitude of the police not only reflected this complete apathy, but it also had additional communal bias. Even after the riots, no action was ever taken against Thackeray or any of the other culprits.

Vir Sanghvi on his blog: Personal charisma, astuteness and a sense of timing accounted for Thackeray’s longevity