Matthew Johnston

 was a Vault 51 dweller who perished under ZAX's rule. A personal trainer before the War, he was used by ZAX to engineer discord and strife between Joel Chambers and his wife, Elizabeth Chambers. An innocuous suggestion to look after Elizabeth's health led to an affair between the trainer and the state senator's wife. The affair came to a head next year, in August 2078, when Joel shot Matthew after his wife strangled his lover, Carmen Greene, before he and his wife murdered each other.

Appearances
is mentioned only in Fallout 76.