Atlas was Hermes’s maternal grandfather in Greek mythology.
Hermes was the son of Zeus and Maia. Maia was one of the Pleiades, the seven daughters of the Titan Atlas and the Oceanid Pleione. Through Maia, Atlas was therefore Hermes’s maternal grandfather.
Atlas is usually described as a Titan rather than a river god. He was condemned to bear the heavens on his shoulders after the Titanomachy, the war between the Titans and the Olympian gods. This makes Atlas a particularly important figure in Hermes’s maternal ancestry.
A common mix-up is confusing Atlas with Oceanus. Oceanus was a primordial Titan associated with the world-encircling stream of water, while Atlas was Maia’s father. Pleione, Maia’s mother, was an Oceanid, which helps explain why several water-related names can appear in accounts of the Pleiades’ genealogy.