Gregory John Mahlberg (born August 8, 1952) is an American former professional baseball catcher, manager and coach.

He threw and batted right-handed, stood 5 feet 10 inches (1.78 m) tall and weighed 185 pounds (84 kg).

[citation needed] He was signed by the Texas Rangers as an undrafted free agent in 1973 and appeared briefly in Major League Baseball for the Rangers in 1978–79, collecting two hits in 18 at bats for an .111 career batting average.

His lone Major League home run came off left-hander Floyd Bannister on September 3, 1979.

He began his managing career in the Seattle Mariners farm system in 1983, and spent 15 years as a minor league pilot, also working for the Chicago Cubs, Milwaukee Brewers and Tampa Bay Devil Rays.