(written from a Production point of view)
Visual effects (VFX) technician Donald "Don" Edmund Trumbull (27 May 1909 – 7 June 2004; age 95) was a VFX specialist who has worked on Star Trek: The Motion Picture in 1979, officially credited for "Mechanical Design". He was known in later life to friends and colleagues as "Pappy Trumbull", to distinguish him from his by then famous son Douglas Trumbull, who worked concurrently as VFX director on the movie.
That father and son were working together on the movie was not a case of nepotism, but rather one of coincidence; Donald was working for Apogee, Inc. at the time, the company that was brought in during the early days of March 1979 by Douglas to alleviate the work pressure on his own company, Future General Corporation (FGC), resulting from that movie's February 1979 VFX debacle.
Career outside Star TrekEdit
Hailing from the Mid-West, Don Trumbull moved in the 1930s to Hollywood to work as a VFX technician in the motion picture industry. Prior to the mid-1950s, it was neither customary to mention effects vendors nor its employees in the end-credit roll of a motion picture production. The extent of Trumbull's motion picture contributions for the 1930s period is therefore hard to ascertain, yet it is known that he has worked as an uncredited special effects rigger on the 1939 classic fantasy movie The Wizard of Oz.
Having an engineering background, his skills were a highly sought after commodity when World War II broke out, and he started to work for the aviation industry, where he focused his talents on engineering hydraulics, pneumatics and special tooling, and pioneered the development of the mixing and application of epoxy sealants for aircraft and automobiles, earning 19 patents.  Upon war's end he has remained in the employment of the aviation and automotive industries.
Approaching retirement age in 1971, he was asked by his son to help out with the design and construction of the endearing Huey. Louis and Dewey robots on the 1972 cult science fiction movie Silent Running, for which his father constructed the articulated robot arms.   Until then, son Douglas had not even been aware of his father's prior Hollywood career as he recalled in 2011, "He had a tremendous influence on me, although when he was first in the movie business as a young man working on The Wizard of Oz and some other movies, I was just a twinkle in his eye, I didn’t know anything about that at the time. By the time I was conscious he was already out of the movie business and in the aircraft industry. My relationship with him throughout my life as a young man was that he was an engineer and inventor. I always hung about where he worked at home and I was surrounded by his machine tools, lathes, mills, drill presses, pedal saws and welding machines. So I grew up surrounded by technology." 
Donald Trumbull stayed on in the motion picture industry, joining Industrial Light & Magic in the mid 1970s, helping out former co-worker on Silent Running, John Dykstra – and a former protégé of Douglas Trumbull and referred by him to George Lucas for Star Wars – , with the engineering and mechanical aspects of his advanced computerized filming rigg for the filming of studio models, utilized to great effect for the first, 1977, Star Wars film. A hugely influential piece of cinematographic equipment, it became the very foundation of modern motion control photography, which he elaborated upon when he subsequently helped out his son and his company FGC again for the 1977 classic science fiction movie Close Encounters of the Third Kind.
The following year Don Trumbull rejoined Dykstra to work on, what was to become, the pilot episode of the original Battlestar Galactica science fiction series in 1978. During that production, Dykstra founded his own company, Apogee, Inc., and invited the elder Trumbull to become full partner, which he accepted, only to find himself working again with his son one year later on the company's subsequent project, The Motion Picture. Trumbull senior has remained in the employment of Apogee for the rest of his working life, having worked on such movies as Firefox (1982), Lifeforce (1985, featuring Patrick Stewart), Spaceballs (1987) with the 1991 movie Rock-A-Doodle as his last recorded credit, all of which in some sort of VFX engineering function.
While his son has become the more famous member of those in the family working in the motion picture industry, the contributions of the elder Trumbull in his second Hollywood career – which, being on the technical side, habitually has remained somewhat in the shadows – has not gone unnoticed with the The Academy of Motion Picture Arts and Sciences who awarded him with two technical Academy Awards in 1988 (citing, "For the design and development of the "Blue Max" high-power, blue-flux projector for traveling matte composite photography. ") and in 1999 (citing, "For advancing the state-of-the-art of real-time motion-control, as exemplified in the Gazelle and Zebra camera dolly systems.") respectively, incidentally tying him with his more famous son in Academy Awards actually won.
Trumbull passed away in 2004 from natural causes in the home of one of his daughters, having been preceded in death by his wife of fifty years, Carroll Roy, the year previously and being survived by five children, of which Douglas was the only son, eighteen grandchildren and ten great-grandchildren.