Former Liverpool, Aston Villa and France manager Gerard Houllier has died aged 73.
Houllier spent six years at Anfield between 1998-2004, winning four major trophies including the League Cup, FA Cup and UEFA Cup in 2001.
After two years with Lyon, Houllier returned to the Premier League in 2010, replacing Martin O'Neill as manager of Aston Villa. He stepped down from his role at Villa Park in June the following year, shortly after falling ill with heart problems.
The Frenchman spent 38 years as a manager, also taking charge of the France national team, Lyon and Paris Saint-Germain, where he won Ligue 1 in 1986 - the first of PSG's nine titles.
In a statement on Monday, Liverpool said: "Liverpool FC is mourning the passing of former manager Gerard Houllier, aged 73.
"The Frenchman was in charge of the Reds for six seasons, leading his team to an historic and unforgettable treble of League Cup, FA Cup and UEFA Cup in 2000-01 and returning the club to the Champions League.
"Houllier - who recovered from life-saving heart surgery during the 2001-02 campaign to return to the dugout - later guided Liverpool to a second League Cup triumph of his tenure in 2003 and departed the following year having overseen 307 matches and successfully re-established the club as a modern force.
"Everybody at the club is deeply saddened by the loss of Gerard and our thoughts are with his family and friends."
Former Liverpool striker Michael Owen paid tribute to Houllier on Twitter, writing: "Absolutely heartbroken to hear that my old boss, Gerard Houllier, has sadly passed away. A great manager and a genuinely caring man."
Jamie Carragher said he was "absolutely devastated" by the news of Houllier's death. The former defender wrote on Twitter: "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 and as a player and got LFC back winning trophies. RIP Boss."
Jamie Redknapp wrote on Instagram: "Incredibly sad news to hear of the passing of Gerard Houllier. A man that did an amazing job for Liverpool football club and for football as a whole. My thoughts and prayers go out to his family. I will never forget the day he gave me the Liverpool captaincy the greatest honour of my career. R.I.P Gerard."
Roy Evans, who was joint manager with Houllier for four months in 1998, had this to say: "Incredibly sad news hearing of the passing of Gerard Houllier. A gentleman I have the greatest respect for and what he achieved at Liverpool football club. Condolences to his family. RIP."
Incredibly sad news hearing of the passing of Gerrard Houllier. A gentleman I have the greatest respect for and what he achieved at Liverpool football club. Condolences to his family. RIP— ROY EVANS (@Roy_Evo) December 14, 2020
Very sad news about Gerard Houllier. He was a gentleman and a great footballing person; I enjoyed his company many times. His legacy at LFC will forever be appreciated, respected and never forgotten. Marina and I offer our sincere condolences to his family. RIP Gerard. YNWA— Sir Kenny Dalglish (😷) (@kennethdalglish) December 14, 2020
Sir Alex Ferguson said: "The news has come as a total shock this morning. Gerard Houllier was still a young man at the age of 73.
"Gerard became a really good friend during his time at Liverpool. We remained great friends after he left and he was always a great ally to have.
"He had fantastic football knowledge which he gained during his extensive and varied career. When we saw each other at UEFA meetings or other events, we would often enjoy a chat, he was always great company and I will miss him dearly. He was a true gentleman.
"It is a sad day for the football world and my thoughts are with his family at this desperately sad time."
Aston Villa added on Twitter: "All at Aston Villa are deeply saddened to learn of the passing of Gerard Houllier, our manager during the 2010/11 season. Our thoughts are with Gérard's loved ones at this incredibly difficult time."
Former Liverpool forward Ian Rush tweeted: "Devastated at the passing of Gerard Houllier. A true gentleman of the game, always put others first @LFC #RIP.
Stephen Warnock, who played for Houllier at Liverpool and Aston Villa, told Sky Sports News: "He's someone who had a huge influence at Liverpool and the French national team as well. He was my manager on two occasions, both at Liverpool and Aston Villa. This is terrible news.
"He'll be remembered fondly by Liverpool fans for that incredible season where they won the treble and went on to win five trophies under Houllier in the calendar year. It was a quite remarkable season.
"He was a stern disciplinarian. He brought new standards into Liverpool when he first came in. He was very similar to Arsene Wenger, when he came into Arsenal and how he tried to implement a different diet and way the players should live. You only have to listen to Steven Gerrard, Danny Murphy, Jamie Carragher talk about the influence he had on their careers and how he changed their set up to approach football and the way they lived their life. He had a huge influence on their careers.
"He did have that disciplinarian side to him, that a school teacher perhaps has, and he had that in and around the training ground. He was very stern in the way he spoke. But tactically he was very astute and a huge studier of the game. He changed Liverpool after Roy Evans and tried to bring a different style in, a continental style into Liverpool and that worked for a period of time.
"He made very big decisions at Liverpool but that was something he was never afraid to do. Never afraid to make those decisions. At Liverpool it was a big thing at the time because you had big characters in the changing room but he wasn't afraid of those characters, he wasn't afraid to do what he thought was right for the football club to move it forward."
Liverpool skipper Jordan Henderson tweeted: "A great man and a great manager. Liverpool will be forever grateful. Gerard Houllier - Repose en paix", while Steven Gerrard said on Instagram: "I will never forget what this man did for me and my career. Rest in peace Boss."
Just heard the sad news of gerard houllier’s passing ... a sad day for football .. condolences to his family.🙏🏾— John Barnes (@officialbarnesy) December 14, 2020
Manchester United also posted their sympathy on Twitter and there were further messages from across football.
Our thoughts are with the family and friends of former Liverpool manager, Gerard Houllier, who has sadly passed away at the age of 73.— Professional Footballers' Association (@PFA) December 14, 2020
Gerard was an innovative football thinker, who had a big impact on English football. pic.twitter.com/WgujX96NWH
The Premier League is saddened to learn that former Liverpool and Aston Villa manager Gérard Houllier, has died at the age of 73— Premier League (@premierleague) December 14, 2020
Our thoughts and condolences are with Gérard’s family and friends at this difficult time: https://t.co/MmUIxLn7GA pic.twitter.com/80lgIQJUYn
Manchester City manager Pep Guardiola added his thoughts: "It is sad news. All of Manchester City send deep condolences to his family.
"He was an incredible, lovely person when I met him in UEFA meetings or when we played against Lyon.
"I first met him when I was at Barcelona and we played the UEFA Cup against Liverpool when he was manager.
"It's sad for all of football."
President of the French Football Federation Noël Le Graët said: "French football is losing one of its greatest technicians, and the French Federation one of its most loyal servants.
"Gérard Houllier has distinguished himself at all levels of football: in the amateur world as a player then coach, in the professional world as coach of reputable clubs, in the Federation as National Technical Director and coach of the French team.
"Thanks to his unanimously recognised technical qualities, Gérard Houllier was a wonderful teacher, open-minded, warm, accessible, deeply human.
"French football owes him a lot. I address, on behalf of the Federation, to his family and loved ones our heartfelt thoughts and our deepest condolences."
Analysis: Houllier restored Liverpool to the top table
Gerard Houllier adored Liverpool and his role in bringing glory days back to Anfield should not be overlooked. The cup successes of 2001 made it one of the more remarkable years in the club's history as Liverpool won the League Cup, FA Cup, UEFA Cup, Charity Shield and European Super Cup.
Houllier not only gave supporters some wonderful memories, he helped restore Liverpool's status among Europe's elite.
For a generation of fans, the fallow period in the 1990s now feels like a blip but when Liverpool qualified for the Champions League in 2001, it took the club back into Europe's premier club competition for the first time since the Heysel disaster of 1985.
Houllier's avuncular appearance masked a steely determination. His high standards of professionalism helped to pave the way for the greater successes that were to follow under Rafa Benitez, making improvements at Melwood, modernising behaviour and tactics.
Liverpool's second-place finish in the 2001/02 season was the club's best in over a decade and would not be bettered for almost another two. His passion for the club lasted for the rest of his life - well beyond his departure in the summer of 2004.
There were later roles, including at Aston Villa. He will be remembered too for his work in developing a special generation of French talent at Clairefontaine, even being awarded the Legion d'honneur for his services to French football.
But it is for those memorable successes in 2001 - and the wide-eyed joy with which he greeted them - that British football will surely remember him best.