Geoffrey Mandel was a Starfleet officer who was listed as a member of Research and Development on the dedication plaques of the USS Stargazer, USS Titan-A, and USS Enterprise-G. (PIC: "The Star Gazer", "The Next Generation", "The Last Generation")
This character was only mentioned in writing.
It can be presumed that this individual was named after production assistant Geoffrey Mandel.
Mandel was also listed on being a member of Fleet Ops at the Utopia Planitia Fleet Yards on the dedication plaque of the USS Odyssey. This plaque was made for the Star Trek: Deep Space Nine episode "The Jem'Hadar", but did not make an appearance in the episode. The plaque can be viewed at the Twitter account of DS9's writer and producer Ira Steven Behr. [1]