In late 2265, Mathews attended Lieutenant Lee Kelso's memorial service that was held in the ship's chapel. He sat on the front-row and was accompanied by his colleague, Edward Rayburn, Lieutenant Stiles and Captain Kirk. (TOS - My Brother's Keeper novel: Constitution)
Sometime in 2266, the real Mathews was killed and replaced by a Klingon agent, that was supposed to spy on Captain James T. Kirk and the Enterprise in the build-up to war. (TOS - Errand of Vengeance novel: The Edge of the Sword)
Later that year, Mathews and Rayburn accompanied Captain Kirk and Christine Chapel to the surface of Exo III to ascertain the location of Doctor Roger Korby's archaeological expedition. Both security officers were killed by the android Ruk. (TOS episode: "What Are Little Girls Made Of?")
- Mathews first name wasn't established in his one screen appearance in TOS episode: "What Are Little Girls Made Of?". The name Ethan was first established in the TOS - Errand of Vengeance novel: The Edge of the Sword, as well as the fact that he was also killed and replaced by a Klingon agent prior to the episode.
- In both novels, Mathews was misspelt as Matthews.