Tarvos or Saturn XXI is a non-spherical moon of Saturn. It was found by John J. Kavelaars, et al. on September 23, 2000, and given the designation S/2000 S 4. The name, given in August 2003, is after Tarvos from Gaulish mythology.
Tarvos orbits Saturn at an average distance of 18 million km in 926 days and is about 15 km in diameter (assuming an albedo of 0.04).
It is a member of the Gallic group of non-spherical moons.
Sharing similar orbit and displaying similar light-red colour, Tarvos is thought to have been formed in a break-up of a bigger body or to be a piece of Albiorix.