Mark Geyer is an Australian radio host and former professional rugby league footballer who played in the 1980s, 1990s and 2000. An Australian international and New South Wales State of Origin representative second-rower, Geyer's club career was played primarily with Penrith, with whom he won a premiership in 1991, as well as the Balmain Tigers and the Western Reds. One of the most controversial figures of the 1990s, Geyer's talent as a second-row forward was more than matched by his aggression on the field which often saw him cross paths with officaldom.

In 1987, Geyer established a regular first-grade place with the Penrith Panthers and was selected for the City Seconds team after only a handful of top-grade appearances. He also played in Penrith's 1987 Reserve Grade Grand Final winning team. Geyer was first selected in the second row for New South Wales in Game III of the 1989 State of Origin series, at Lang Park in Brisbane.

His 1990 season was largely lost to a succession of injuries that restricted him to just 12 games, though he did play in Penrith's maiden Grand Final appearance (an 18–14 loss to the Canberra Raiders) and from there was selected, along with Panthers teammates Greg Alexander, John Cartwright and Brad Fittler, for the 1990 Kangaroo tour. Geyer played in 11 games on the Kangaroo Tour, scoring four tries and earning his first Australian test jumper when he was selected on the bench.

Geyer's form for the Panthers in 1991 again earned him selection for NSW during the State of Origin series. Geyer received a five-match suspension for an incident in the second game at a wet Sydney Football Stadium, which was preceded by a half-time confrontation with Queensland captain Wally Lewis in which referee David Manson and NSW captain Ben Elias had to stand between the two, who twice almost came to blows. He was cited for an elbow to the head of Queensland fullback Paul Hauff, which sparked an all-in brawl. Suspension would blight Geyer throughout his career as he often struggled to contain his aggressive tendencies.

In August 1991, he was thought to be out for the rest of the season after injuring his ankle ligaments in a training session, only to return for the major semifinal. However, despite his problems during the season, Geyer helped the minor premiers into the Grand Final where they gained revenge on Canberra with a 19–12 victory that saw the Panthers win their first premiership since entering the competition in 1967. Geyer had a hand in all three of the Panthers tries on the day and was judged to be their best player, though his sin-binning for dissent by referee Bill Harrigan during the second half was thought to have cost him the Clive Churchill Medal as man of the match.

He spent the 1993 season with the Balmain Tigers. After leaving Penrith in controversial circumstances, the coach of Balmain at the time Alan Jones handed Geyer a lifeline. In 1994, Geyer spent a season playing with the Umina Beach Bunnies who play in the Central Coast Division Rugby League competition after leaving Balmain. Geyer played for the Western Reds from 1995 until 1997, before returning to the Panthers in 1998 where he re-established his career with three good seasons. He retired at the end of the 2000 season.

In 2012, it was announced that Geyer would join Fox Sports Australia as part of their Rugby League coverage. On Australia Day 2013, Mark was announced in the Honours List. He received an Order of Australia medal for "service to the sport of Rugby League football, and to the community through a range of charitable organisations. Geyer's younger brother Matt Geyer also played rugby league, initially with Mark at the Western Reds in 1997, before playing with the Melbourne Storm between 1998 and 2008.