The English language began with three tribes: Angles, Saxons, and Jutes, invading Britain back around 450 A.D. Before these tribes, there were natives already inhabiting the land, the Celts.
Tribal Roots to Old English:
Angles, Saxons, & Jutes
When the Angles, Saxons, and Jutes came, they pretty much conquered and pushed the natives (Celts) back to the west side of the “island”.
The Angles, Saxons, and Jutes spoke Old English, a West Germanic language that was closely associated (linguistically) with Frisian (Anglo-Frisian is the technical term). Other languages include Flemish, Dutch, Afrikaans, German, and Yiddish.
Old English is rooted from West Germanic languages. Old English sounded similar to German, with guttural utterances and throaty sounds.
Britain had been a province of the Roman empire 400 years prior to the arrival of these tribes. This is important to note because while the Celts fought with mostly the Saxons, the Romans fought with the Angles; hence historians dubbed the label of these three tribes “Anglo-Saxons” (sorry Jutes, you got left out).
Latin had a small impact on Old English, a couple thousand borrowed words. Celtic did not (less than 200) due to the lack of social integration (Celts were often either enslaved or driven West).
Interesting fact: Celts moved west, the language became “Welsh” from the Old English word “wealas” meaning foreigner. Unfair considering the Celts were the real natives to the land, the Anglo-Saxons were not.
Alright, brief timeline:
443 A.D- Roman legionnaires “left” Britain
455 A.D- Angles, Saxons, and Jutes begin conquest over Britain
601 A.D- “Angli” referred to Britain people by Romans (Pope Gregory the Great) (540 A.D- 604 A.D)
731 A.D- Saint Bede the Venerable wrote “Historia ecclesiastica gentis Anglorum” (Ecclesiastical History of the English People)
So there you have it, a very basic understanding of the history/origin of English.