Clifford Charles Devlin Thorburn (born 16 January 1948) is a Canadian retired professional snooker player. Nicknamed "The Grinder" because of his slow, determined style of play, he won the World Snooker Championship in 1980, defeating Alex Higgins 18–16 in the final. He is generally recognised as the sport's first world champion from outside the United Kingdom—since Australian Horace Lindrum's 1952 title is usually disregarded—and he remains the only world champion from the Americas. He was runner-up in two other world championships, losing 21–25 to John Spencer in the 1977 final and 6–18 to Steve Davis in the 1983 final. At the 1983 tournament, Thorburn became the first player to make a maximum break in a World Championship match, achieving the feat in his second-round encounter with Terry Griffiths.

Ranked world number one during the 1981–82 season, Thorburn was the first non-British player to top the snooker world rankings. He won the invitational Masters in 1983, 1985, and 1986, making him the first player to win the tournament three times and the first to retain the title. He retired from the main professional tour in 1996. Inducted into Canada's Sports Hall of Fame in 2001 and the Snooker Hall of Fame in 2014, he competed later in his career in Snooker Legends events and on the World Seniors Tour, winning the 2018 Seniors Masters at the Crucible Theatre at age 70. He retired from competitive snooker after the 2022 UK Seniors Championship.

Thorburn was born on 16 January 1948 in Victoria, British Columbia. His parents separated when he was eighteen months old. He was abandoned by his mother, and after spending about two years in an orphanage during a custody dispute, was raised by his father and his paternal grandmother. He was told that his mother had died, but, aged twenty, learnt that she was still alive.

He played pool and lacrosse in his youth, and set a one-game scoring record of ten goals in the Greater Victoria Minor Lacrosse Association "midget division" in 1958. He left school at the age of 16, and travelled across Canada playing pool and snooker money matches, taking jobs as a dishwasher and working on a garbage truck to help earn money for his stakes. In 1968 he entered his first tournaments, and won the Toronto City Championship. He spent time with Fred Davis and Rex Williams when they toured Canada in 1970, and afterwards became a resident professional at the House of Champions club in Toronto.

In July 1970, he reportedly made a maximum break of 147 in a non-competitive game against Fred Hardwick. He made six century breaks in winning the North American Amateur Championship in 1971, equalling the record, jointly held by Joe Davis and George Chenier, for most century breaks in a single tournament.

Thorburn played John Spencer in a series of three exhibition matches in 1971; although he lost all three, he was recommended by Spencer to the World Professional Billiards and Snooker Association, and he was accepted as a professional in 1972. Thorburn travelled to England in 1973, and on the day of his arrival, the reigning world snooker champion Alex Higgins offered to play him for £5 a frame. Thorburn, receiving 28 points start in each frame, claims to have beaten Higgins in every frame they played, and that Higgins refused to pay up.

At the 1973 World Snooker Championship, his first major tournament on the professional snooker circuit, Thorburn defeated Dennis Taylor 9–8 in the first round then lost 15–16 to Williams in the second round. Later that year, he had a 4–0 win over Pat Houlihan at the 1973 Norwich Union Open before losing 2–4 to Higgins in the quarter-final. In the 1974 World Snooker Championship he defeated Alex McDonald 8–3 in qualifying then lost 4–8 to Paddy Morgan in the first round. He started the 1974–75 snooker season with a victory in the 1974 Canadian Open, knocking out Willie Thorne and Graham Miles to reach the final, where he won 8–6 against Taylor. He reached the quarter-finals of the 1975 World Snooker Championship with wins over Morgan and Miles, losing the quarter-final 12–19 to Eddie Charlton, and, the following year, was eliminated 14–15 by Higgins in the first round of the 1976 World Snooker Championship.

The 1977 World Snooker Championship was the first to be held at the Crucible Theatre in Sheffield. Thorburn became the first Canadian world snooker championship finalist. He whitewashed Chris Ross 11–0 in qualifying, then recorded a 13–6 win over Williams. In the quarter-final, he won in the deciding frame, 13–12, against Charlton. He overcame Taylor 18–16 in the semi-final, and twelve hours later was facing Spencer in the final. Spencer built a 4–2 lead at the end of the first session, but Thorburn won four of the next six frames and they finished the second session level at 6–6. Thorburn took the first two frames of the third session, and it finished with them level again, at 9–9. Thorburn built a 13–11 lead during the fourth session, and extended it to 15–11 before Spencer won four consecutive frames to make it 15–15; the next session again saw them share the frames, finishing at 18–18. Spencer won three frames in a row to lead 21–18, and Thorburn took the next two to trail by a single frame. Spencer took the last frame of the session, leading 22–20. In the last session, Thorburn again narrowed the gap to one frame, but then Spencer won three in a row to achieve victory at 25–21.