Onesilus (alternatives: Onesilos, Onisillos) (Greek: Ονήσιλος) (died 497 BC) was the brother of king Gorgos (Gorgus) of the Greek city-state of Salamis on the island of Cyprus. Cyprus was a part of the Persian Empire but when the Ionians rebelled from Persian rule, Onesilos used the occasion to capture the city of Salamis and usurp his brother’s throne; he was able to win every city on the island except for the Graeco-Phoenician city-state of Amathus, which stayed loyal to the Persians.