Captain Harris was a 23rd century Starfleet officer who served as the commanding officer of the Federation starship USS Excalibur during the late 2260s.
In 2268, Harris commanded the Excalibur during the disastrous M-5 Starfleet battle simulation war games. When the M-5 malfunctioned in control of the USS Enterprise, commanded by James T. Kirk, it caused the Enterprise phasers to fire full-power on the other ships that participated in the games, severely damaging the unshielded Excalibur, Harris and his first officer died early in the conflict, and all of the ship's approximately 400 crewmen were eventually lost.
The M-5 recorded, at Kirk's request, that no life remained aboard the hulk of Excalibur. (TOS: "The Ultimate Computer")
This character was only mentioned in dialogue.
Captain Harris was given the first name Paul in Who's Who in Star Trek 2. The novel After the Fall calls him Anton Harris.