This is a list of characters from the TV sitcom Red Dwarf.

Ace Rimmer (Commander Arnold Judas Rimmer) is an alter-ego of Arnold Rimmer, also played by Chris Barrie. Ace first appears in the episode Dimension Jump and is the antithesis of Rimmer, modest despite being a popular, knowledgeable daredevil hero. He comes from a seemingly "perfect" universe, in which Rimmer and Lister lived happy, successful lives and were good friends.

Ace's childhood paralleled Rimmer's up-until the age of seven, when one of them was kept down a year at school while the other was not. The one kept down became Ace, who claims that the shame of being a clear foot taller than the rest of his class inspired him to buckle down, fight back, and work hard, while Arnold spent the rest of his life making excuses for his many failures.

A red dwarf is a small and relatively cool star on the main sequence, either late K or M spectral type. They have a mass of less than half that of the Sun (down to about 0.075 solar masses, below which stellar objects are brown dwarfs) and a surface temperature of less than 4,000 K. Red dwarfs are by far the most common type of star in the Galaxy, at least in the neighborhood of the Sun. Proxima Centauri, the nearest star to the Sun, is a red dwarf (Type M5, apparent magnitude 11.05), as are twenty of the next thirty nearest. However, due to their low luminosity, individual red dwarfs cannot easily be observed. From Earth, none is visible to the naked eye.

Stellar models indicate that red dwarfs with less than 35% of the Sun's mass are fully convective. Hence the helium produced by the thermonuclear fusion of hydrogen is constantly remixed throughout the star, avoiding a buildup at the core. Red dwarfs therefore develop very slowly, having a constant luminosity and spectral type for some hundreds of billions of years, until their fuel is depleted. Because of the comparatively short age of the universe, no red dwarfs of advanced evolutionary stages exist in the current era.