Doug Mountjoy (8 June 1942 – 14 February 2021) was a Welsh snooker player. He was a mainstay of the professional snooker circuit during the late 1970s and 1980s, and remained within the top 16 of the world rankings for eleven consecutive years. He began his professional snooker career by clinching the title at the 1977 Masters tournament, which he had entered as a late replacement. He won both the 1978 UK Championship and the 1979 Irish Masters, and reached the final of the 1981 World Championship where he lost to Steve Davis. He also finished in second place at the 1985 Masters, but by 1988 he had dropped out of the top 16.
Mountjoy enjoyed a resurgence in his 40s, and at the age of 46 he defeated future seven-time world champion Stephen Hendry in the final of the 1988 UK Championship. He followed this up with the 1989 Classic title, and by the end of the 1988–89 season he was back in the top 16, where he remained until 1992. His world ranking peaked at #5 in 1990/1991. He also won five Welsh Professional titles during his career.
Diagnosed with lung cancer in 1993, Mountjoy qualified for the World Championship at the age of 50, just weeks before having a lung surgically removed. He continued to play professionally until 1997, and he was coach to the United Arab Emirates snooker association between 1997 and 1999.