
He was the chairman of the Welsh Automotive Forum, professor emeritus and president of the Centre of Automotive Industry Research at Cardiff University and an adviser to Welsh Government on economic and automotive affairs.
He died in his sleep at his Cardiff home on February 21, a week before his 77th birthday, and he is survived by his wife and three children.
Welsh Automotive Forum chief executive Tim Williams said: "Garel's death has been a tremendous shock to all in the forum and I know the sadness will be shared throughout the automotive community as we extend our very deepest and sincere condolences to his family."
Mr Williams added: "His passing will be felt around the world, where he extensively lectured and spoke at events. His unrivalled international standing made him the natural and really the only choice to help establish the Welsh Automotive Forum in 1997 and after it was incorporated Garel became chairman in 2001. He then fought tooth and nail to voice the concerns of the supply chain and automotive industry through some of the toughest times in recent history.
"He was a wise counsellor, often taking an alternative view to the popular train of thought on an issue, but he was invariably right in the end. Those who listened to his keynote speeches relished his presentation style of no-nonsense facts blended with that irrepressible Welsh humour which made him so commanding and enjoyable.
"With his encyclopedic knowledge of the Welsh automotive industry from the dawn of the motor car to the present day, I think it is fair to say we will not see his like again, and he will be sorely missed by hundreds if not thousands whose lives he touched during a very full life."
Prof Rhys was awarded Welsh Motoring Writers' most prestigious honour, the Tom Pryce Trophy, in 2002.
Welsh Motoring Writers chairman Huw Thomas said: "He was an almost impossible act to follow for his breadth and depth of knowledge. Although he was an economist by academic discipline he had a real enthusiasm for the automotive sector - the industry, its brands and products including their history and heritage, as well as the motor trade
"He was very much a social animal. He was open and engaging and loved a chat. He was a Welshman through and through, and the Wales automotive sector was very much close to his heart."