Professor Leo Brownell was a male Human and a noted member of Starfleet in the 2240s, holding the rank of admiral and occupying a faculty position at Starfleet Academy as one of Starfleet's leading minds in engineering and computer science.
At the time of the NX-1701 prototype's planned first mission and shakedown on reference stardate 1/83, Professor Brownell was on loan from Starfleet Academy to supervise final fitting out of the starship's systems, and serve as it's chief engineer during the emergency mission to rescue the passengers of the disabled SS Rosenberg. Ironically after the mission, the very ship he just served on for the mission would be commissioned and christened under April as the USS Enterprise.
Captain Robert April noted that Brownell was a "Starfleet institution", and a greater asset to Starfleet than the starship itself. In his career, Professor Brownell was responsible for formulating the combination of dilithium intermix reactions and newly developed duotronic systems to enable continuous flight at warp drive speeds, as previously ship's computers and sensors were unable to keep up with the calculations necessary for warp speed travel, requiring frequent stops or blind flight. (TOS novel: Final Frontier)