In Greek mythology, Megareus referred to two different people

1. King of Megara With the aid of Apollo, Alcathous rebuilt the walls of Megara, for which Megareus, gave him his daughter, Periboea, as a wife.
2. King of Onchestus in Boeotia, father of Hippomenes. He was part of the Seven Against Thebes and committed suicide in response to a claim by the oracle Tiresias that Thebes would win if one person would voluntarily die to save it.