Johannesburg - The Falcons Rugby Union's president Samuel "SJ" de Beer died in the early hours of Monday morning, the SA Rugby Union (SARU) said in a statement.
De Beer, who would have been 58 next month, had a long struggle with cancer.
"SJ was one of the stalwarts of club and provincial rugby in South Africa, the type of rugby man without whom our game would wither at the grassroots level," said SARU president Oregan Hoskins.
"He gave selflessly to our game and was dedicated to his task when taking responsibility for duties within our committees.
"He was a gentleman in all he did and we will miss him greatly."
De Beer, a lawyer by profession, played for the former Eastern Transvaal and also coached the Falcons Under-21 team before rising to the presidency in 2008.
He was a director of the Falcons company and served on the union's disciplinary committee for a number of years.
De Beer is survived by his wife, Hettie, four children and four grandchildren.