David Arkham was a crewman on board the Excalibur.
When the Excalibur came across a derelict alien ship, Arkham, along with many of the crew were possessed by mind-altering aliens. The alien who was influencing Mr. Welles, in retaliation of Captain Matthew Gideon's attempts to drive out the aliens, had the alien removed from Arkham's body and then had him shot.
After the crisis, Gideon dictated a message to Arkham's father, telling him of his son's sacrifice.[1]