MacWilliams was a male human and one of the miners aboard the JMC mining spaceship Red Dwarf, killed in the radiation leak which killed all but one of the crew in the pilot episode.
At some point in the late 22nd century, Red Dwarf visited Miranda, and some of the crew went down for planetary shore-leave. At the "Hacienda" astro space bar, Second Technician Arnold Rimmer drunkenly voiced aloud the rumour that fellow crewmember MacWilliams was "in favour of sleeping with the dead" right to MacWilliam's face, when he was with four of his biggest mates. This caused a bar room brawl, and Rimmer was "out the door quicker than a whippet with a bum full of dynamite", and leaving Dave Lister to face the music alone.
Three million years later, Lister used the event with MacWilliams and the bar room brawl as an example of how Rimmer was such a basic, natural coward. ("Marooned", Series III)