They were Jutes, a Germanic tribe whose names are preserved today in Jutland and Juteborg. They invaded Britain in the 5th century under the leadership of Hengist and Horsa. The Venerable Bede tells us they occupied the Isle of Wight, parts of the Hampshire coast, and Kent with its capital at Canterbury. They were also Saxons, (Germanic) though they came from the Danish peninsula, and lived partly from piracy from the 3rd century AD to the 5th, when they invaded Britain at the end of Roman supremacy. Their name survives in Wessex, Essex, Sussex and Saxony in Germany itself. The Saxons and Jutes were joined by the Angles, Germanic in origin who probably came from the area of Schleswig-Holstein or neighbouring Denmark. They settled down in East Anglia and Northumbria. Their name survives in the gradual metamorphosis from Anglo-Saxon England to Englaland and thence to England.
These three principal groups were joined by Frisians, Swabians and some settlers from Southern Sweden, though they were all dubbed Anglo-Saxons after settlement.
The first reliable historian in English history was the monk Bede who explained the origins of the independent Anglo-Saxon kingdoms in his Historia Ecclesiastica Gentis Anglorum (come on Latin scholars (!) – ‘Ecclesiastic History of English People’). The East Angles became East Anglia (Norfolk, Suffolk etc.); Middle Angles became the East Midlands; the Mercians developed into the Midlands, while those who settled north of the River Humber were descended from the Angles.
Meanwhile the Saxons established the kingdoms of the East Saxons in what is now Essex, the South Saxons in Sussex, and the West Saxons in Wessex (now called ‘The West Country, much celebrated in the novels of Thomas Hardy). The Jutes as we know settled in Kent, the Isle of Wight and Hampshire.
Just to make things more complicated, way up north in Northumbria under Edwin, Oswald and Oswy, authority over all the Anglo-Saxons was claimed in a Law called Bretwaldaship. By the 8th century this hegemony had passed to Mercia under Ethelbald and Offa, and at last in the 9th century to Wessex, whose kings were able to withstand and in some cases repel the Viking invasions.
With Alfred the Great, Aethelstan, Edward the Elder and Edgar, Wessex established an undisputed claim to the ‘overlordship’ of England, but the renewal of savage Viking assaults from Denmark and Norway led to the crowning of a Nordic king, Canute or Cnut who became King of England in 1016. The West Saxon line was briefly restored with Edward the Confessor in 1042, but everything collapsed with the Norman Conquest under William Duke of Normandy (himself of Viking stock).
The Anglo-Saxons had been pagan races before the conversion to Christianity of Ethelbert of Kent by St. Augustine of Canterbury in 597. Christian progress was rapid, and Canterburywas chosen as the ideal place to build the first major cathedral dedicated to the Christian Church. It was in this church that Thomas Becket was later murdered at the ‘suggestion’ of King Henry II (q.v.). Becket by the way was not Saxon, as is suggested often in plays and films. He was as Norman as Henry II himself.