the word 'seth' was first said as 'set'. because of changes in the egyptian language over the 3,000 years that seth was worshiped, the 't' in set was pronounced so similarly from 'th' that the greeks wrote it as seth during the ptolemaic period. set was originally responsible for protecting ra during his journey in the afterlife, personally slaying the great serpent apep. late period set killed his brother osiris, who had succeeded ra as pharaoh, out of jealousy. horus (osiris and isis' son) eventually defeated set and claimed the throne.