A huge but also hugely divisive figure within the automotive industry as well as amongst enthusiasts of the Italian car brands – Marchionne was famous for eschewing suits, shirts and ties in favour of casual black woollen sweaters that became his trademark.

He was due to officially retire next year, albeit he still planned to retain the Chairman and CEO roles at sportscar maker Ferrari which was spun out of FCA two and a half years ago.

Marchionne was born in Chieti, Abruzzo, Italy, but at the age of 13 his family emigrated to Toronto in Canada and he would later graduate from the University of Windsor in 1979 with a Bachelor of Commerce before earning a law degree in 1983 and finally an MBA in 1985

The first part of his career saw him working in the world of accounting and finance, starting off with Deliotte & Touche, in Canada. He would rise through the ranks to become CEO of Zurich-based Algroup (Alusuisse Lonza Group) in 1997 before being appointed CEO and Managing Director of certification company SGS in Geneva in 2004. SGS would appoint him chairman in 2006.

Marchionne became an independent board member of Fiat S.p.A. in May 2003 just as the Italian carmaker was entering a period of turmoil and a year later he was appointed as CEO (with Luca Cordero di Montezemolo taking the chairman’s role) and with a clear a mandate to rescue the company.

He immediately embarked on a high-profile pursuit of General Motors (GM) which at the time owned a 10% stake in Fiat and was liable to purchase the remaining 90% thanks to an infamous ‘put’ option that was held in Fiat’s favour meaning the Italian carmaker could exercise it once the due date arrived.

Eventually Marchionne secured a massive US$1.99 billion payout from GM in February 2005 in exchange for cancelling the option which gave the Italian company an important financial lifeline and he was widely lauded for making the deal.

On being appointed CEO Marchionne had immediately set about restructuring the ailing carmaker, bringing a fresh international prespective and he generally managed to avoid major redundancies amongst the workforce across Italy although the small Termine Imerese plant in Sicily would soon be discarded.

His first big product hit came in 2007 with the launch of the new Fiat 500 although the outline of the project preceded him although Ford, which was part of a joint venture that saw the 500 and Ford’s own Ka sharing platforms, financed the bulk of the project, another coup for Marchionne. The 500 was an instant hit right across Europe and provided much needed revenues. He also oversaw some duds, such as the Fiat Croma, which he pushed into production against the advice of most people, and Dodge's compact sedan, the Dart.

However, his big deal came in April 2009 when he eyed up a merger with Chrysler as it slid into Chapter 11 bankruptcy protection and was bailed out by the U.S. government. Initially Fiat purchased a 20% stake when Chrysler emerged from the Chapter 11 period two months afterwards, with the UAW union as well as the U.S. and Canadian governments’ being the other stakeholders.

Gradually Fiat built its shareholding up before taking full control in January 2014, listing on the stock market as Fiat Chrysler Automobiles, and later a full merger between the two companies would take place.

In the merged company Marchionne started to focus primarily on the stateside market and in particular on the Jeep and Ram (the latter which he split away from Dodge) brands. The volume Fiat brand was starved of investment and new models and saw its market share shrink across the world, notably in Brazil where under Marchionne’s watch Fiat lost its number one status and recent investments have gone towards Jeep.

That focus on the US market though disguises his lack of success in the world's biggest car market, China, where FCA is today far behind the curve with a litany of failed joint ventures and a minimal market share although this year it's again trying to kickstart its presence, this time with the Jeepbrand.

In Italy, so long the market that underpinned Fiat’s fortunes, FCA is this year languishing at historic lows. He also began producing smaller Jeep models in Italy for European markets as part of a strategy to take the Jeep brand global – which so far is progressing well and in fact it was the Jeep division boss Mike Manley who was elected by the FCA board to replace Marchionne as CEO last Saturday.

He was credited with leading FCA away from sedans and investing in SUVs and crossover segment vehicles, growing in popularity with customers, particularly clearing out capacity in the U.S. to build more Ram trucks, although the market's steady movement in this direction that's been boosted by low oil prices played into the hands of the Jeep and Ram brands. However, that strategy of putting all the eggs in one basket of bigger and less efficient vehicles is wholly reliant on oil prices remaining low.

He also signed up to a unique joint venture with Mazda to rework its small convertible sportscar for sale by the Fiat brand, which revived the famous "124" nametag, and this stylish model has generally been very well recieved. Rebadging Mitsubishi's Triton pickup for the Fiat Professional division was another project that has also given Fiat a ready made contender in a new market segment.

Towards the end of 2015 Ferrari was spun out of FCA and listed on the New York Stock Exchange. At the end of 2014 Marchionne had ousted Montezemolo as Chairman and CEO of Ferrari after a 23-year reign and he started to take a hands-on approach to the company and in the running of the legendary ‘Scuderia’ F1 team, appointing a new Team Principal and becoming involved in decision making.

That final season with Montezemolo in charge, 2014,was the Scuderia's worst in 20 years and they in fact failed to win a single race since 1993. The Scuderia showed a steady return to winning fortunes under Marchionne's guidance, fighting hard for the title last year while they are right in the hunt once again at this year's halfway point.

Marchionne has also very publicly battled this year with the new F1 owners, Liberty Media, on the direction they want to take the sport in the future and, just like Enzo Ferrari and Montezemolo before him, has several times threatened to pull Ferrari out of F1 if he didn't get what he wanted.

He also returned the Alfa Romeo name to F1 this year after a three decade absence, albeit this time coming in as a title sponsor of the Sauber team and he had openly discussed a similar branding arrangement to bring Maserati back, this time aligned with the American Haas team. Both teams race with Ferrari engines.

CEO and Executive Chairman of the Formula One Group, Chase Carey, said today: "We are deeply saddened by the passing of Sergio Marchionne. He was a great leader of not just Formula 1 and the automobile world, but the business world overall. "He led with great passion, energy and insight, and inspired all around him. His contributions to Formula 1 are immeasurable. He was also a true friend to all of us and he will be deeply missed."

Marchionne gained a reputation over the years for outlandish sales volume targets that were never reached and presentations that threw up rafts of future models that rarely ever appeared – or did so years late.

He also continually pursued the idea of a merger with another OEM, particularly with GM although he was always – publicly at least – rebuffed, believing that FCA did make the volumes to survive in the long-term future and constantly predicted industry consolidations which as yet haven’t occurred. Creating a bigger player through industry consolidation was always his number one objective from the start and in this strategy he was certainly a failure, rivals not only seeing direction differently but also being put off by his management style.

With his accounting background he continually pushed to create shareholder value and improve profits and was generally very well respected by analysts. “Marchionne was hired to fix Fiat in 2004 when the Italian carmaker was worth $7.5bn,” said the Financial Times’ Henry Foy today in a Twitter post. “Today he died, with Fiat, Chrysler and Ferrari worth roughly 10 times that. He was the smartest man I ever interviewed, and the car industry will never replace him.”

In recent years Marchionne changed tack from a clear focus on volume brands and relaunched the languishing Alfa Romeo and Maserati divisions, with both receiving several key new models such as the Giulia (sedan) and Stelvio (SUV) for the former and the Ghibli (sedan) Levante (SUV) for the latter, although the revivals have suffered from botched model launches, poor overall direction and sales that haven’t come anywhere near expectations – or profitability. Large sums have been frittered away on these projects which will never be recouped. With much work needing to be done for both brands this will be one of the first decisions for Manley to get to grips with.

He also brought Fiat first and then later Alfa Romeo back to the U.S. after a long absence from this market. They have both had a lukewarm reception so far although Alfa Romeo seems to be gaining some traction now with the Stelvio.

He cut off the Lancia brand following a dismal attempt to rebadge Chrysler models fell flat on its face and the historic brand is now reduced to a single rapidly fading model, the Ypsilon, and just one market, Italy.

Marchionne also missed out on the industry’s big move towards electrification, firstly dismissing it and more recently, after understanding the market’s accelerating shift, jumping on board – but FCA languishes far behind the curve and has no strategy or investment to go forward and play catch up.

On 21 July he was replaced in all his positions at FCA where Manley took over the CEO’s role and at Ferrari where FCA Chairman and Agnelli family representative John Elkann was appointed Chairman while Louis Louis Camilleri, the former chairman and CEO of Philip Morris International and a current Ferrari board member, became the CEO. He was also replaced at SGS and CNH Global, the latter being the tractor-to-trucks manufacturer that was formally part of Fiat Group.

Manley said today: “Clearly this is a very sad and difficult time. Our thoughts and prayers go out to his family, friends and colleagues. There is no doubt that Sergio was a very special, unique man, and no doubt he will be sorely missed.”

Mary Barra, the Chairman and CEO of General Motors who had long rebuffed Marchionne’s overtures towards a merger paid tribute today: "We at General Motors offer our condolences to Sergio Marchionne's family and friends. Sergio created a remarkable legacy in the automotive industry. Our thoughts are also with our industry colleagues at Fiat Chrysler as they deal with this sudden loss."

John Elkann in a statement issued by the Agnelli family’s investment company EXOR today said: "Unfortunately, what we feared has come to pass. Sergio Marchionne, man and friend, is gone. I believe that the best way to honour his memory is to build on the legacy he left us, continuing to develop the human values of responsibility and openness of which he was the most ardent champion.”