John A. Theisen (born 9 May 1961; age 51) is a role playing game designer and writer for FASA and GDW from the mid-1980s through to the early 1990s. He worked on Star Trek and Mechwarrior for FASA and Space: 1889 for GDW. In addition to this, he wrote a number of articles for various gaming magazines. He was credited with writing and design on eight supplements in the Star Trek line, and "timeline assistance" on one other, "The Federation". He also taught Star Trek briefly at the New Mexico State University--Carlsbad.

He currently lives and works in Phoenix, Arizona for a government agency, where he is involved in research, statistics, policy and contract compliance, trend analysis, and emergency preparedness.