In Greek mythology, Hermione was the daughter of Menelaus, king of Sparta, and Helen of Troy. Betrothed first to her cousin Orestes, she was later promised to Achilles' son Neoptolemus as a prize of the Trojan War. After Neoptolemus' death at Delphi she married Orestes and bore Tisamenus, continuing the Spartan-Mycenaean royal line.
Adapted from Wikipedia, "Hermione (mythology)" · CC BY-SA 4.0
I.Betrothals
Before the Trojan War, Tyndareus betrothed Hermione to Orestes. Apollodorus says she was nine when Helen left with Paris. During the war Menelaus promised her instead to Neoptolemus; Euripides' Andromache has Orestes call Menelaus a liar for that switch, while Ovid's Heroides has Hermione insist Tyndareus acted without Menelaus' knowledge.
Homer's Odyssey places her wedding to Neoptolemus ten years after Troy: when Telemachus visits Sparta, Menelaus is holding the marriage feast as he sends his daughter to Achilles' son.
II.Neoptolemus and Andromache
At Phthia Hermione quarreled with Andromache, Hector's widow and Neoptolemus' war-prize concubine. In Euripides she blames Andromache's spells for her own childlessness and seeks to have her killed while Neoptolemus is away at Delphi; Peleus intervenes.
Neoptolemus dies at Delphi — slain by a priest, temple servants, Apollo, or by Orestes, according to variant accounts. Orestes then takes Hermione to Mycenae to fulfill the original betrothal.
III.Marriage to Orestes
Hermione and Orestes marry; their son Tisamenus becomes heir of the Atreid line in the Peloponnese. Some notices also give Orestes a marriage to Erigone, without clarifying Hermione's fate. Later lore places Hermione with her parents in Elysium; a scholion on Pindar, citing Ibycus, even has her marry the apotheosized Diomedes among the Dioscuri.
Her story fed later art and drama, from Racine's Andromaque to Rossini's Ermione.