Ephialtes was also the name of the greek from Trachis who betrayed the Spartans
to the Persians
at the battle of Thermopylae
A bounty was placed on his head in 488B.C. by the Delphic Amphictiony the international organisation that oversaw affairs at Delphi. He spent ten years in Thessaly. He was murdered in 478B.C. on his return to Trachis by a fellow Trachinian, who killed him for personal reasons. The Spartans honoured the man who killed him as a hero.
A different Ephialtes was one of the giants who attacked Mount. Olympus
. He was apparently killed by Apollo and his bow.