Clifford Luyk Diem (born June 28, 1941) is an American-born former basketball player who played professionally in Spain and Europe from 1962 to 1978. He played college basketball for the University of Florida. He was drafted by the New York Knicks of the National Basketball Association (NBA), but never played a regular season game in the NBA. He signed with the Spanish professional team Real Madrid, helped Real Madrid become the dominant European basketball team of the 1960s, and is remembered for his trademark, old-school hook shot.
Luyk was born in Syracuse, New York, to a Dutch-born father and a Swiss-born mother. He attended Vernon-Verona-Sherrill High School in Verona, New York, where the 6-foot, seven-inch Luyk became the star center for the VVS Red Devils high school basketball team. As a senior in 1957–58, he scored 488 points in 18 games for an average of 27.1 points per game.
Luyk joined Real Madrid in 1962, and became a naturalized Spanish citizen three years later. He retired in 1978, having won six Euroleague titles with Madrid's legendary club (1964, 1965, 1967, 1968, 1974 and 1978, despite not playing in the 1978 final). This record makes him unique: he is the only player who has won six Euroleague titles as a player with the same team. Luyk also won 14 Spanish Championships, 10 Spanish Cups, and two Intercontinental Cups.
Following his 1978 retirement as a player, Luyk became a coach. From 1978 to 1981, he coached the Real Madrid junior team and never lost a game. After that, he worked as a Real Madrid assistant coach under head coach Lolo Sainz for six seasons from 1983 to 1989, and for another season under head coach George Karl from 1989 to 1990. He returned to Real Madrid as head coach from 1991 to 1994, and won two Spanish League championships, a Saporta Cup and a King's Cup. Coached by Luyk, Real Madrid lost to Limoges CSP in the Euroleague Final Four in 1993. He again served as Real Madrid's head coach during the 1998–99 season, and has been a technical adviser to the club since 2009.
Luyk is married to Paquita Torres Pérez, a former Miss Spain (1966) and Miss Europe (1967), in 1970. Luyk and Torres had three children, one of whom, Sergio, played college basketball for St. John's University, and later played professionally for Real Madrid. Their daughter Estefania is a professional model.