As the story goes, ZeuS cohabited with Leda in the form of a swan on the same night as her husband, king Tyndareus. To the former she gave birth to Helen and Pollux, and to the latter, Clytemnestra and Pollux. In some versions she laid eggs from which the children hatched.
Helen's unsurpassed beauty attracted a lot of attention, and she had suitors from all over Greece. In fact, these are essentially the same as the Greek champions at Troy - with the notable exceptions of AgaMemnon? and AchillEus - for fearing they would come to blows Tyndareus required each to take an oath to protect her marriage. With that done, she was married to Menelaus, and on the deaths of her brothers (the DioScuri?) they succeeded to the Spartan throne.
In TheIliad, Helen is described as god-like, and this refers not just to her looks but also to her disregard for other people. So it came to pass that when Paris arrived at Sparta and was received kindly by Menelaus as a guest, she fell in love with him - he had been promised her hand by Aphrodite - and willingly escaped with him to Troy, abandoning her husband and nine-year-old daughter Hermione.
Menelaus was furious, and begged his brother Agamemnon, king of Mycenae, to raise an army. Her suitors were reminded of their oaths, and other champions too were invited to join the expedition. Thus began the TrojanWar?, celebrated in legend, that lasts ten years and leads to the distruction of Troy. Homer presents Helen as intensely remorseful, finally aware of the consequences of her actions and the suffering she has wrought but too late to avert it.
Afterwards Helen returns with Menelaus to Sparta. Despite all the damage she has caused and the curse on the house of Atreus, the two seem to live happily ever after. According to most versions, their only child was Hermione, who marries Agamemnon's son Orestes.