Prometheus is the ring shepherd moon that orbits inside Saturn’s F ring opposite Pandora. Its gravity helps confine and shape the narrow ring, while Pandora orbits outside it.
Prometheus is an irregular, potato-shaped moon only about 100 kilometres across. Its orbit is slightly eccentric, so its gravitational interaction with the F ring can create waves, channels, and other changing structures in the ring’s material.
The moon was discovered in photographs taken by Voyager 1 in 1980, although some images from the earlier Pioneer 11 encounter also contained it without leading to an immediate identification. Prometheus received its mythological name because Saturn’s moons are commonly named after figures from classical mythology.
Prometheus is easy to confuse with the Titan who stole fire for humanity, but the question concerns a physical moon of Saturn. Pandora, the other shepherd, lies outside the F ring and works as the paired outer influence.