Wall Streeters used to ask Damian Lewis, the actor who plays ruthless money manager Bobby Axelrod in hit drama series Billions, if his character was based on hedge fund billionaire Bill Ackman "all the time".
For a start, the pair share initials. And like Axelrod, Ackman is also a familiar in Wall Street gossip pages, has a property empire in the Hamptons made up of four separate addresses and has had public feuds with rival billionaires (New York hotspots are said to be careful to separate Ackman and business magnate Carl Icahn if they are in the same vicinity).
But Lewis denied that Axelrod was based on any real person (though his character is thought to be loosely modelled on Steven Cohen at SAC Capital). Instead, Ackman is taking up a starring role in Britain as he becomes the FTSE 100's newest chief executive.
After its stock climbed over 100pc since listing in 2017, hedge fund Pershing Square is replacing Homeserve on the blue-chip index, catapulting Ackman into the limelight as one of Britain's big company bosses.
He is one of the biggest names in American finance circles, with a current charity auction showing that people would pay over $65,000 just for lunch with him (there is still four days to go before the winning bidder is announced). However, Ackman, who has over 178,000 Twitter followers and whose bets have landed him a fortune of over $2.2bn (£1.9bn), is lesser known in the UK.
The Harvard graduate founded Pershing in 2003 and is one of the most outspoken figures on Wall Street. After moving his family out of New York at the start of the year due to coronavirus fears he went on to warn Donald Trump in March that the only way to control the virus was to shut America for 30 days. He told CNBC around the same time that "hell is coming". His firm made over $2bn betting that markets would crash.
The 56-year-old, who relaxes through meditating and reportedly practices intermittent fasting to keep healthy, is considered an activist investor who pressures the companies he invests in to change.
His high-profile battles have included a public spat with American payroll giant ADP, which Pershing called a "lethargic and inefficient sleeping giant" in a 168-page report. ADP's boss Carlos Rodriguez then retaliated by calling the hedge fund manager a "spoiled brat" during a TV interview.
He was also once Herbalife's most outspoken critic, calling the health drinks firm a pyramid scheme which cynically targeted low-income communities. His $1bn campaign against the business ended in him nursing years of losses.
In 2018, after three years of losses from soured bets, Reuters reported that the billionaire was looking to lower his public profile in a major change of tack. A staff cull also included the loss of his personal driver, leaving Ackman to get the train to work instead.
But 2020 has been one of the best years for Pershing, with a return of around 55pc, so it is likely that the hedge fund titan's days on public transport are over. As will be any attempts to keep a low profile - being a chief executive on the FTSE 100 comes with intense public scrutiny, particularly if you are one of America's best-known billionaires.