Imogen is the beautiful and wise daughter of Cymbeline the King of Britain. She incurs the displeasure of her father because she marries the low born Posthumus:
"His daughter, [Imogen] and the heir of's kingdom, whom
He purposed to his wife's sole son--a widow
That late he married--hath referr'd herself
Unto a poor but worthy gentleman[Posthumus]: she's wedded;
Her husband banish'd; she imprison'd: all
Is outward sorrow; though I think the king
Be touch'd at very heart."
The Queen and Imogen's villainous stepmother wanted her to marry her stupid son Cloten so that she could eventually become Queen of England.