The 73-year-old, who also managed Aston Villa, Olympique Lyonnais (Lyon) and Paris St Germain (PSG), passed away after having a heart operation in Paris, L’Equipe said.
Liverpool FC tweeted on Monday: “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. Rest in peace, Gerard Houllier 1947-2020.”
The club also posted a lengthy tribute on its website, calling Houllier a “revolutionary and vital figure in Liverpool’s modern history”.
Sky Sports pundit and former Liverpool star Jamie Carragher said on Twitter he had contact with Houllier last month, whom he “loved to bits”, and was “devastated” at the passing of a man who changed his game and the club.
Former England striker Michael Owen, who played under Houllier at Liverpool, 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.”
Gary Lineker, who played for Merseyside rivals Everton, called him one of the “smartest, warmest and loveliest people in football”.