Former France and Liverpool manager Gerard Houllier died on Monday at age 73.
RMC Sport and French sports daily L'Equipe said Houllier had died after having a heart operation in Paris.
RMC Sport said it is "saddened to learn of the death of Gerard Houllier, who passed away during the night, at the age of 73. Our thoughts are with all those close to him."
Houllier managed Liverpool for six years from 1998 and guided the Reds to a historic treble of FA Cup, League Cup and Uefa Cup in 2001.
"We are mourning the passing of our treble-winning manager, Gerard Houllier. The thoughts of everyone at Liverpool Football Club are with Gerard’s family and many friends," a message on Liverpool's Twitter account said.
He also coached at Paris Saint-Germain and Lyon in his homeland before his final managerial assignment in England with Aston Villa was terminated in 2011.
Former Liverpool striker Michael Owen, who scored two goals to win the 2001 FA Cup final against Arsenal when Houllier was in charge, was among many leading figures in English football to pay tribute to the Frenchman.
Owen wrote on Twitter: "Absolutely heartbroken to hear that my old boss, Gerard Houllier, has sadly passed away. A great manager and a genuinely caring man. #RIPBoss".
Former Liverpool defender Jamie Carragher said: "Absolutely devastated by the news about Gerard Houllier, I was in touch with him only last month to arrange him coming to Liverpool.
"Loved that man to bits, he changed me as a person & as a player & got @LFC back winning trophies. RIP Boss."
After an unheralded playing career in France's lower leagues, Houllier began coaching in 1973, earning his first big job with Lens before taking over at Paris Saint-Germain.
He became France's assistant coach in 1988 and then manager in 1992 but had a short, unsuccessful spell in charge.
He resigned after failing to take the team to the 1994 World Cup in the United States following shock home defeats by Israel and Bulgaria, losing the latter game, which they only needed to draw to qualify, 2-1 after a goal in added time.
Houllier initially arrived at Anfield in July 1998, joining the club as co-manager with Roy Evans.
Evans resigned on November 10, leaving Houllier in sole charge, from where he rebuilt a side that had been labelled the "Spice Boys" by UK media known as much for their lifestyles off the pitch as their skills on it.
Under the Frenchman's guidance the Reds became a more rounded unit which culminated in an unprecedented five trophies in 2001, with the Charity Shield and Uefa Super Cup also secured.
In October that year, Houllier underwent emergency heart surgery after falling ill on the bench during a Premier League fixture against Leeds United.
He returned to the dugout after five months, and with the help of assistant Phil Thompson, led the club to a second place finish in the 2001/02 season.
Houllier left Liverpool in 2004, having also overseen an overhaul of the club's youth system, being replaced by Rafa Benitez.
He returned to France to take over at perennial Ligue 1 champions Lyon, guiding them to back-to-back titles in 2006 and 2007
In September 2008 Aston Villa appointed Houllier as manager after Martin O'Neill resigned the previous month.
However, Houllier's spell at Villa Park was cut short due to illness, forcing him to step down from his role after just nine months.
Former Villa and England striker Darren Bent wrote on Twitter: "R.I.P Boss, You will be missed. Could not speak highly enough of you, not just as a manager but as a person as well. Taught me to see things Differently. Condolences to the Houllier family."