Gregory Jein was a Chinese American model designer.

Jein collaborated with visual effects master Douglas Trumbull on Star Trek: The Motion Picture (1979), Star Trek V: The Final Frontier (1989), Star Trek VI: The Undiscovered Country (1991), Star Trek: Insurrection (1998) and Star Trek X: Nemesis (2002) and the Star Trek shows The Next Generation, Deep Space Nine and Voyager.

His work with Trumbull began with a three-month assignment at the Future General Corp. His major contribution as chief model maker to Close Encounters of the Third Kind was the ethereal Mothership. (The model is now housed in the Smithsonian's Steven F. Udvar-Hazy Center.)

Much of his work was done through his company, Gregory Jein Inc., which he launched in 1979.

He shared Emmy nominations for the 1996 Deep Space Nine episode "Trials and Tribble-ations" and for the 2003 HBO miniseries Angels in America, and he received eight excellence in production design nominations from the Art Directors Guild.

Jein shared visual effects Oscar nominations with Trumbull, Roy Arbogast and brothers Matthew and Richard Yuricich on Close Encounters of the Third Kind (1977) and with William A. Fraker and A.D. Flowers on 1941 (1979).

He worked on the NBC telefilm The UFO Incident and the Wonder Woman pilot for ABC in 1975.

His most recent contribution as a model maker was for the live-action Mulan (2020).

Jein died May 22, 2022 in Los Angeles, California. He was 76.