Gregory Allan Gibson (born October 2, 1968 in Ironton, Ohio) is an umpire in Major League Baseball who has worked in the National League from 1997 to 1999 and throughout both major leagues since 2000. Throughout his career, he has worn the number 53 on his uniform. Gibson has worked five Division Series (2001, 2003, 2004, 2006 and 2007), one League Championship Series (2005) and the 2008 All-Star Game. He was the home plate umpire for Randy Johnson's perfect game on May 18, 2004. Before reaching the major leagues, he umpired in the Appalachian League (1991), Florida Instructional League (1991 and 1994), South Atlantic League (1992), Florida State League (1993), Eastern League (1994-1995) and International League (1996-1999).
On September 3, 2008, Gibson was the home plate umpire for MLB's first use of instant replay.
Gibson's crew for the 2008 season includes Kerwin Danley, Brian Runge and Charlie Reliford (crew chief).