Aethra or Aithra was the daughter of King Pittheus of Troezen. Aethra was the first wife of King Aegeus and the mother of Theseus by either Aegeus or Poseidon. She is also has a long association with Helen of Troy.
When Theseus grew up, he kidnapped Helen. She was then brought to Aethra to look after, but Helen's brother Dioscuri (other accounts mention Castor and Pollux) rescued her. Helen and her brother(s) took Aethra captive and as a sign of revenge, they forced her to work as Helen's handmaid.