Robb is Ned Stark's oldest son. He went to war with the Lannister family after his father was executed. Robb's main goal is rescuing his sisters, Arya and Sansa, whom he believes are being held captive by the Lannisters. (Sansa is, but Arya has actually escaped.) Robb's advisers advocated that the North become its own country, independent of the Lannisters, so he now holds the title of the King of the North. He recently married a battlefield nurse, Talisa, despite the fact that he had already agreed to marry the daughter of a lord – an alliance that would have given him permission to cross through the lord's territory.
In season one, Robb's forces captured Jaime Lannister and held him as a captive. In season two, however, Robb's mother, Catelyn, released Jaime and sent him – in the custody of a female knight named Brienne – to the capital, hoping that he could be traded for her daughters. She did so without telling Robb and Robb, furious, has since ordered that she be kept under guard at all times.