John Garman Hertzler Jr. (born March 18, 1950, in Savannah, Georgia) is an American actor, author, screenwriter, and activist best known for his role as the Klingon General (later Chancellor) Martok on Star Trek: Deep Space Nine, a role he played from 1995 until the series ended in 1999.

Hertzler began his acting career in the 1970s, primarily in stage acting and some films, eventually guest-starring in TV shows before landing a major role in the 1990s series Zorro as Alcalde Ignacio De Soto. Beyond Deep Space Nine, he appeared in several other Star Trek shows, wrote two Star Trek novels, and frequently appeared at science fiction conventions.

He grew up mostly around Washington, D.C., attended Bucknell University (earning a degree in political science), pursued a master's in set design at the University of Maryland, and even attended law school briefly. His early career included theater in Washington, New York, San Francisco, and Southern California, with roles spanning Shakespeare and other dramatic works, as well as some film appearances.

Hertzler lives in the Finger Lakes region of New York, where he has lectured at Cornell University’s theater department and has been active in local politics and writing screenplays.

His filmography includes notable appearances outside of Star Trek, such as Quantum Leap, Zorro, Highlander, and others.