Growing up on the Main Line, Mateer was first noted for his tennis skills, excelling at the sport at Episcopal Academy and Haverford College, from which he graduated in 1950 with a degree in engineering.
His graduating class accumulated four successive Middle Atlantic League championships and a four-year record of 45-6. He reached the second round of the 1951 U.S. National Championships, losing in the first round in 1948.
But as a squash player, he tore up the courts in the decades of the 1950s and '60s.
He was a two-time intercollegiate champion, set a record as 11-time U.S. National Doubles champion and was the only amateur to win the North American Open twice.
He was inducted into numerous halls of fame, including those of the U.S. Squash Rackets Association, U.S. Intercollegiate Association, Episcopal Academy, Maryland Squash and the Haverford College Glasser Hall of Achievement.
Mateer often teamed up with his sons Gil and Drew to win doubles championships.
Fans were fascinated in the late '50s by Mateer's rivalry with Henri Salaun. According to the Daily Squash Report, they split six national finals, with Mateer's titles in 1954, 1956 and 1960, while Salaun prevailed in 1955, 1958 and 1961.
Mateer was a handsome, clean-cut athlete who charmed his fans with his boyish manner, sense of humor and fair play.
"Mateer's game, like the man himself, was built along clean and classic lines and had an all-American golden-boy feel to it," the Daily Squash Report wrote.
"Blond, muscular and handsome, he was blessed with great power, size, mobility, touch and all-around athleticism, and his fundamentally sound strokes were developed in squash's mecca, the Merion Cricket Club."
Mateer and his rival, Salaun, appeared on the cover of Sports Illustrated on Feb. 10, 1958.
Mateer was a retired executive with the Mateer Co., which manufactures powder and liquid filling machines and was founded by his father in 1946.
His 41-year marriage to the former Joan Sommer ended when she died in 1993. He married Ann Eldridge in 1994.
Besides his wife and sons Drew and Gil, he is survived by two other sons, Diehl Mateer III and Jeff Mateer; a daughter, Carver Mateer Severance; a sister, Sally Chisholm, and 13 grandchildren.
Services: Memorial service 10 a.m. Oct. 4 at St. Mary's Episcopal Church, Wayne.
Contributions may be made to the American Cancer Society, Box 22718, Oklahoma City, OK 73123-1718.
Contact John F. Morrison at firstname.lastname@example.org or 215-854-5573