Queen Emma (called Aelfgifu by most of her subjects) was a strong-willed Norman who was queen of England twice over--first as the wife of Anglo-Saxon king Aethelred, then as the wife of the conquering Danish king Cnut. She had little impact in Aethelred's court, but was (according to O'Brien) very involved in revitalizing Cnut's reputation in Europe through conspicuous acts of piety and generosity. After Cnut's death, she fought long and hard to get one of her sons on the English throne. Cnut's two sons, Harold Harefoot (son of Cnut's first wife, also named Aelfgifu) and Harthacnut (Emma's son) each claimed the throne, but Harold died and Harthacnut was crowned King of England without having to fight. Emma's younger son by Aethelred then returned to England (he had been hiding in Normandy) and joined his half-brother Harthacnut as co-ruler. Harthacnut was a brutal and heavy-handed ruler, and few mourned when he died only a few years later. Edward, later called "Confessor", was then the sole ruler of England. Upon his childless death many years later, Emma's nephew William the Conquerer claimed the throne.
It's fascinating history, but there is frustratingly little known about Emma herself. Today, we only have a few clues, from The Anglo-Saxon Chronicle
and the history she commissioned, the Encomium Emmae