"I first played against Keith 46 years ago when Wales played Ireland, and that was the start of a close friendship that we kept going down the years.
"We didn't talk much on that first meeting but I got to really know him in 1962 on the British and Irish Lions tour to South Africa when he was something of an elder statesman and I was one of the newcomers.
"My great friend was Ken Jones and Keith was like a father figure to us. I got to know Keith better than many others on that tour and, once our playing careers finished, we kept in close touch down the years.
"When I joined the IRB in 1994, Keith was the General Secretary of the organisation, which was then based in Bristol. He played a huge part in the reorganisation of both the IRB and Rugby World Cup and the movement of those entities to Dublin.
"Keith spent a lot of time in Dublin handling the organisation and, driven by his great passion for the game - always a great advantage when devoting your life to something like that, he was able to cope with the politics of the world game and proved a most accomplished administrator.
"Keith left a marvellous legacy for those who followed him, whilst also being a magnificent friend."
Bernard Lapasset (President FFR)
"Keith was a great, great member of the rugby family who left his mark on the world game. His commitment was always 100 per cent and he gave great service to the game.
"As a player he was tough, hard and strong - always very difficult to play against. As an administrator he was the man who showed me the ropes at the IRB. He was my mentor.
"The way he worked on the Rugby World Cup was very impressive. He was a very proud Welshman who loved his country. And he was incredibly generous in his service to the game.
"The thoughts of everyone in French rugby go out to his family at this time. Our game has lost a great servant."
Syd Miller (Former Lions team-mate and current chairman of the IRB)
"I first saw Keith playing for Wales just before he was picked to tour with the Lions in 1962. There was this very large second row who we had never heard of. He came to the Welsh team very late, yet he was still good enough to be picked for the Lions tour.
"His contribution to the Lions in South Africa was immense. He was a large man, capable of matching the huge Springboks in physicality, but he was also a very skilful player.
"His life was all about giving service, he was a well rounded individual who committed time to others. He became the first CEO of the IRB and he was one of the people whose vision put the Rugby World Cup in place.
"We owe a debt of gratitude to him for that, but Keith also left behind a legacy at the IRB. As an organisation we have benefited from his involvement.
"His contribution to the 1999 Rugby World Cup was considerable. There were a few problems and he sorted them out. He was a good friend and I am very sad that he has gone. Our thoughts are with his family at this time."
Sir Brian Lochore (ex-All Black captain, coach and team manager)
"I was in the All Blacks tour party in 1963, although I didn't play against Cardiff when Keith was in their side. Yet I can recall watching him in that game. I remember him vividly as a Lion in South Africa in 1962 because he was uncompromising in his play. As a man and as a player he was always the same - a very big and strong personality.
"As All Blacks coach, I had a lot to do with Keith during his time at the IRB. Next year will be the third Rugby World Cup in which I've been involved. At the first two, 1987 and 1995, Keith had a huge impact.
"He was 'Mr IRB' and he did a tremendous job for world rugby. I believe a big reason for that was the respect and support he gained around the world - and certainly in New Zealand. He was a total gentleman."
Derek Morgan (Wales Secondary School team mate, England international and former President of RFU)
"The first time I came across Keith was in a line-out when my school, Lewis, Pengam, played Aberdare Grammar School. My second row colleague, David Pask, looked up at the giant opposite him and asked me what the hell was he going to do to win the ball.
"I thought of a few things and did my best to try to stop Keith dominating the line-out, but it didn't work. We went on to play together for the Welsh SS against England in 1955."