Angus ("Gus") Goodman travelled with the Fifth Doctor. Goodman was murdered by an assassin hired by Josiah W. Dogbolter, marking a harsh tone for one of the Doctor's first encounters with the businessman. While many considered him a companion not worth remembering, the Doctor disagreed. His death eventually pushed the Doctor to revealing Dogbolter's corruption to the public, ending a monopoly of evil and corruption.
Gus was an American fighter pilot from a timeline in which World War II was still being fought in 1963. The Fifth Doctor had intended to take the TARDIS to a holiday spot on another world. It instead materialised on an island in the Pacific Ocean of that parallel Earth on 25 July 1963. Gus had crashed on the island after a dogfight with a Japanese plane. (COMIC: Lunar Lagoon) Discovering the Doctor, he put a pistol to his head, but accepted the Doctor's offer to take him off the island. (COMIC: 4-Dimensional Vistas)
As was usual for the Doctor, he did not take Gus home by the direct route. Back in the Doctor's own universe, they first encountered the Doctor's old enemy, the renegade Time Lord known as the Monk, who had allied himself with Ice Warriors to create a gigantic sonic cannon. (COMIC: 4-Dimensional Vistas)
After thwarting their plans, the two travelled to the planet Celeste, where they were captured by the malevolent, frog-like businessman, Josiah W. Dogbolter. The Doctor had offended Dogbolter by refusing to sell the TARDIS to him, so Dogbolter sent the Moderator, a hitman, after him. Just as the Doctor had dropped Gus off at somewhere like his home, the Moderator ambushed them and shot Gus. In the ensuing hail of gunfire, Gus shot and incapacitated the Moderator. Gus died from his wounds. The Doctor left Gus where he had fallen, but eventually encountered Dogbolter again. (COMIC: The Moderator)
Dogbolter didn't remember killing Gus and when reminded by the Twelfth Doctor, referred to Gus as a "nobody". The Doctor, however, had remembered him for centuries and it drove him to finally bring down Dogbolter. (COMIC: The Stockbridge Showdown)