Clarence Thurston McLaughlin, oilman, rancher, and philanthropist, was born on January 31, 1897, in Arthurs, Pennsylvania, one of five children of John Mark and Cora (Griffith) McLaughlin. His father was an oil producer in the fields of western Pennsylvania, and the children attended the public schools in Shippenville, located near the world's first oil town, Titusville. When the United States entered World War I in 1917, McLaughlin served with the 503rd Aero Squadron. Following twenty-five months of military service, he bought a train ticket to Texas with his discharge money to try his hand in the oil industry there. In 1919 he became a partner in a drilling company based in Wichita Falls. Within two years the company was operating several rigs, and McLaughlin introduced the Diamond M logo. On August 6, 1921, he married Evelyn Claire Littleton, a schoolteacher from Knoxville, Tennessee, who had come to Wichita Falls as an employee of Miller Pipeline Company. The couple had three daughters and a son.
During the 1920s and 1930s McLaughlin drilled in the Permian Basin around Big Spring. In 1935 he purchased a ranch in Scurry County twelve miles southwest of Snyder and named it the Diamond M. He added acreage to the original purchase until the ranch at one time totaled 5,200 acres. McLaughlin experimented with new seed varieties and methods. He stocked his ranch with Hereford cattle and, initially, with sheep. He also raised show horses. The discovery of the Canyon Reef field near Snyder in 1948 brought even more wealth to the McLaughlin family, especially after the Lion County Company's No. 2 McLaughlin was completed on Diamond M land in December at 650 barrels a day. Within the next year drilling crews were bringing in a new producing well on the ranch at an average of every five days. In 1950 McLaughlin built an office building in Snyder. He also purchased the 6,000-acre Kuteman Ranch in southern Parker County in 1950, the 2,300-acre Shamrock Ranch near Colorado Springs in 1953, the 31,000-acre Circle Ranch hear Las Vegas, New Mexico, in 1958, and the 1,459-acre Young Ranch in western Fisher County in 1965. Later, as the oil boom leveled off, the McLaughlins sold several of these holdings, but they kept the Young and Shamrock properties; the latter, in Colorado, was expanded to about 5,000 acres and became a second home for the family.
As early as Beauford Jester's 1946 campaign for governor, McLaughlin became interested in state politics and served on the Texas Democratic Executive Committee. In 1956 he was the party's director of finance. He often hosted parties at the Diamond M Ranch for state and national Democratic party leaders, numbering among his guests such luminaries as Coke Stevenson and Lyndon B. Johnson. McLaughlin served on the Texas Hospital Board (1944–48), the Texas Technological College Board of Regents (1948–54), the Texas Public Safety Commission (1960–66), and for fifteen years the advisory board for the Southwest Legal Foundation. In 1949 he established the Diamond M Foundation, financed by royalties from his ranch, for the support of various education and philanthropic undertakings. Through this foundation the Diamond M Museum, featuring the art treasures he and his wife had collected since 1921, was opened at his Diamond M office building in 1964. Because of his interest in western art, McLaughlin was named to the art committee of the National Cowboy Hall of Fame and Western Heritage Center in Oklahoma City. He also was on the first board of directors of the Petroleum Museum, Library, and Hall of Fame, near Midland. He died on July 29, 1975, and was interred beside his wife in Hillside Memorial Gardens near Snyder.