(written from a Production point of view)
Gregory "Greg" J. Barnett (born 17 April) is a stuntman, stunt coordinator, and director who served as Leonard Nimoy's stunt double in Star Trek IV: The Voyage Home and Star Trek V: The Final Frontier. In Star Trek IV, Barnett also performed stunts as a Starfleet technician. His costume from this appearance was sold off on the It's A Wrap! sale and auction on eBay.  In addition, he served as assistant stunt coordinator for the stunt scene aboard the USS Ranger. According to the IMDb, Barnett also performed stunts on Star Trek: Voyager.
His career as a stuntman began in the 1960s with stints on General Hospital and Days of our Lives and has covered 40 years with almost 300 stunt credits in film and TV to his name including Jaws 2 (1978), Murder She Wrote, Terminator 2: Judgment Day (1991), Buffy the Vampire Slayer (1997), Pearl Harbor (2001), Mission: Impossible III (2006), and Heroes (2006).
He served as stunt coordinator, second unit director, underwater photographer, and as a regular background actor on Baywatch. The show also featured Amy Wheaton, Chip Mayer, Albert Stratton, Martin Squires, Christopher Pettiet, Steven Anderson, Lilyan Chauvin, Marci Brickhouse, and James Horan as guest stars, and Monte Markham as a regular character. He also appeared in The Ultimate Imposter (1979, with Star Trek: The Next Generation/Star Trek: Deep Space Nine's Rosalind Chao, Keith Andes, and Robert Phillips), Samurai (1979; with Michael Pataki, Don Keefer, Walt Davis, Bob Minor, Tom Lupo and Johnny Haymer), They Live (1988, with Jeff Imada, Thelma Lee, and Meg Foster), K-9000 (1991; with Judson Scott, Anne Haney, David Renan, Ted Barba, James H. Burk, Kenny Endoso, Jeff Imada, Dave Perna, Nicholas Shaffer and Lane Leavitt). His stunt acting appearances (some of which were credited) include films such as Midnight Ride (1990), The Perfect Weapon (1991, with Cary-Hiroyuki), Thelma and Louise (1991), Last Action Hero (1993), Beverly Hills Cop III (1994), The 4th Tenor (2002), The Guardian (2006) and Aces 'N' Eights (2008, with Jeff Kober). He has guest starred on TV shows such as Equal Justice (1991), Walker, Texas Ranger (1993, with Noble Willingham), The Pretender (1997), Standoff (2006), Vanished (2006) and Mob City (2013).
More recent work includes stunt performances for various Fast and Furious film sequels and stunt coordinating TV shows such as The Mentalist (2012-2014), Ray Donovan (2013, with Denise Crosby), Hart of Dixie (2013-2015), Hit the Floor (2013-2016), Castle (2013-2016, produced by Rob Bowman), Switched at Birth (2011-2017), Baskets (2016-2018) and 9-1-1 (2018-2019).