Who they were
Claiming the throne promised to him, William invaded in 1066 and defeated and killed Harold at Hastings on 14 October. He crushed English resistance — the brutal Harrying of the North in 1069–70 — built castles across the country, replaced the English aristocracy with Normans, and ordered the Domesday Book survey of 1086.
What they did
His conquest tied England to France, brought the French language to the elite and feudal landholding to the whole kingdom, and rebuilt the church under Norman bishops.
Legacy
The Norman Conquest is a hinge of English history: it transformed the language, law, and ruling class, and every English monarch since traces descent from William. The date 1066 is the most famous in English history.