Bates passed away peacefully in Monaco, surrounded by his wife Suzannah and family. Chelsea said in a statement: "It is with great sadness that we share the news of the loss of Ken Bates, former owner and chairman of Chelsea Football Club.
"The club sends our heartfelt condolences to Ken's wife Suzannah, the rest of his family and his friends. Ken's determination to fight for Chelsea when times were tough, and drive the team on to winning trophies will never be forgotten."
Born in west London, Bates made his fortune in business before taking on chairmanships at Oldham Athletic and Wigan Athletic, well before Chelsea came calling. That call came at a moment of genuine crisis: Chelsea had spent most of the 1970s teetering financially, and by 1982 the situation was dire enough that the club's bank was refusing further credit and weighing up which of two cheques to dishonour, a payment owed to the FA or the players' own wages.
The club's financial director brought Bates in to negotiate, and he walked away owning Chelsea for a token £1, inheriting roughly £2million of debt and bringing the Mears family's long ownership of the club to a close.
Results on the pitch were shaky at first — Chelsea only just avoided being relegated into the third tier — but Bates stuck with manager John Neal, and promotion followed soon after, with the club establishing itself as a top-flight fixture. His profile off the pitch grew just as quickly, thanks to blunt, opinionated programme notes and a public manner that made him hard to ignore.
He later won a drawn-out legal fight to secure Stamford Bridge's freehold after developers had taken control of the site, and set up the Chelsea Pitch Owners scheme so supporters could hold a stake in the ground itself.
The most successful period of Bates's chairmanship began in the mid-1990s, as investment from director Matthew Harding helped fund marquee signings including Ruud Gullit and Mark Hughes under manager Glenn Hoddle. Chelsea won the FA Cup twice, along with the League Cup, the UEFA Cup Winners' Cup, the UEFA Super Cup and the Community Shield, while also qualifying for the Champions League and reaching the quarter-finals.
Names such as Gianfranco Zola, Roberto Di Matteo, Marcel Desailly and Dan Petrescu became fixtures at Stamford Bridge, with Dennis Wise lifting silverware as captain, and Bates also oversaw the arrival of academy graduate John Terry and the signing of Frank Lampard. His Chelsea Village project, meanwhile, transformed the stadium and its surroundings with new stands, a hotel, restaurants and other facilities.
Financial pressures returned in the early 2000s, and in the summer of 2003, shortly after Chelsea had again qualified for the Champions League, Bates sold his stake in the club to Roman Abramovich, who went on to acquire full ownership. Bates remained as chairman for a further eight months before resigning, later taking charge of Leeds United, though in his final years he was a regular at Stamford Bridge, watching matches from the directors' box.
Only two men have held the Chelsea chairmanship longer. Bates was never a figure people felt neutral about, and plenty of supporters found his manner difficult over the years, but the fact that Chelsea still exist at Stamford Bridge at all is, in large part, down to him.