(written from a Production point of view)
John Daniel Jefferies, Sr. (8 February 1936 – 25 March 2010; age 74), often credited simply as John Jefferies, was a set designer on Star Trek: The Original Series and brother of Philip and Matt Jefferies. John Jefferies shared credit with Matt, who had brought in his two brothers to help him out with the design work, for designing the original phaser pistol.  John Jefferies also worked on the final construction design for the USS Enterprise. 
Upon termination of The Original Series, John Jefferies obtained ownership of several production assets, including one of small USS Enterprise filming models, as well as one of the two Tholian starship studio models, both of which he had loaned out for display to the 1992 Star Trek Smithsonian Exhibit. However, he, along with his brother Matt, sold off virtually all of their Original Series production items, including his models, still in their possession in the Profiles in History The Star Trek Auction of 12 December 2001, in order to raise funds for the charitable organization "Motion Picture & Television Fund".
Shortly before his passing away, John Jefferies, together with fellow designers Joseph R. Jennings, Herman F. Zimmerman and Scott Chambliss, were honored for their Star Trek contributions in a media event called the "Star Trek Designers Talk Trek History At Art Directors Guild Event", held on 28 September 2009 at the Egyptian Theater in Hollywood, and in which all designer discussed indepth their work on the franchise. The event was moderated by another Star Trek alumnus, Daren Dochterman. 
Career outside Star Trek
Jefferies was born in Richmond, Virginia and grew up in New Jersey. Like his older brother Matt, John was a life-long aviation enthusiast, having owned several airplanes throughout his life and has, again like his brother, also served in the United States Air Force. He began his career in Hollywood following his stint in the air force when he was brought over to the West Coast by his other older brother, Phillip, to join his two brothers, already working there, at a time when there was a shortage of art directors in the motion picture industry. His first project was the 1966 film The Chase, whose cast included Paul Williams. Jefferies' subsequent film work included the 1967 classic Guess Who's Coming to Dinner and the musicals Funny Girl (on which Dick Rubin was property master) and Hello, Dolly! (with set dressings by Craig Binkley). 
Both John and Matt Jefferies work on the 1967 Walt Disney film The Happiest Millionaire. John later worked as a set designer on the 1970 film Catch-22 while Philip Jefferies was the film's art director. During production, Philip became ill and was replaced by Matt. John also took over some of Philip's responsibilities on the film.  On Catch-22, all three brothers were working under production designer Harold Michelson, who later headed the art department on Star Trek: The Motion Picture.
From the 1970s until 2001, Jefferies was an art director and production designer on such television shows as Baa Baa Black Sheep (on which John Larroquette and James Whitmore, Jr. were regulars), The Greatest American Hero, Hardcastle and McCormick (starring Brian Keith and Daniel Hugh Kelly), Matlock, and JAG, the latter of which his last recorded motion picture industry credit. In his later career, he was also a set designer on such films as BASEketball, I Still Know What You Did Last Summer, and Austin Powers: The Spy Who Shagged Me. He was also the art director on the 2001 film Just Visiting, which featured Malcolm McDowell.
Jefferies' daughter married the son of film editor Bruce Schoengarth.
John Jefferies at one time served as president of the International Alliance of Theatrical Stage Employes (IATSE) Set Designers and Model Makers. Jefferies died on 25 March 2010 due to complications from lung cancer. He was 74 years old.