Former UEFA president Lennart Johansson has died at the age of 89.
The Swedish Football Association said that Johansson died after a short illness.
The Swede headed UEFA from 1990 to 2007, and he is most recognised for founding the Champions League in 1992 - a development from what was previously known as the European Cup.
FIFA president Gianni Infantino led the tributes to Johansson.
"I am heartbroken by the news of the passing away of Lennart Johansson," Infantino said, in a statement on the FIFA website.
"He was a friend and an invaluable source of wisdom and inspiration.
"I will be forever grateful for having had him as the president of UEFA when I joined the organisation in 2000. Since then, Lennart has always been a role model of professionalism and, more importantly, of humanity."
Former FIFA president Sepp Blatter posted a tribute to Johansson on Twitter, which read: "With Lennart Johansson we lose a real heavyweight in football.
"We were allies, opponents - even rivals. But in all situations there has been respect and fair play. Thank you for your dedication to our game and to your family. R.I.P."
Swedish FA chairman Karl-Erik Nilsson said: "Lennart Johansson is our greatest international football leader of all time.
"His actions as UEFA president and vice president of FIFA are deeply respected. His leadership is admired the world over.
"I remember Lennart Johansson as a committed and wise leader with an immeasurable integrity, I also remember him as a warm and humorous person with an infinite love of football.
"I met him as recently as a week ago, in connection with the Europa League final in Baku. It was always a hearty meeting, filled with joy and rewarding football discussions."
Johansson was elected as UEFA's fifth president, and he oversaw the organisation's rise in prominence from being an administrative body to a modern sport organisation, based in Nyon, Switzerland.
Johansson also served as FIFA vice-president, but he lost a presidency contest to Sepp Blatter in 1998. He was also president of the Swedish FA from 1984 to 1991, and he had close ties with the AIK Solna club.
UEFA president Aleksander Ceferin said: "UEFA and European football are deeply saddened by the passing of Lennart Johansson, and I would like to express my sincerest condolences to his family and loved ones, as well as to the Swedish Football Association, on their loss.
"He was a devoted lover and servant of football, who put his passion at the heart of his life.
"He will always be remembered as a visionary leader, and as the architect of the UEFA Champions League, and world football will be always be grateful to him for all he has achieved for the beautiful game."
UEFA announced a minute's silence will be observed at the Nations League finals, European qualifiers and under-21 matches taking place this week.