Old English (Ænglisc, Anglisc, Englisc) or Anglo-Saxon is the earliest historical form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers probably in the mid 5th century, and the first Old English literary works date from the mid 7th century. After the Norman Conquest of 1066, English was replaced for a time as the language of the upper classes by Anglo-Norman, a relative of French, and Old English developed into the next historical form of English, known as Middle English. 

The four main dialectal forms of Old English were Mercian, Northumbrian, Kentish, and West Saxon. Mercian and Northumbrian are together referred to as Anglian. In terms of geography the Northumbrian region lay north of the Humber River; the Mercian lay north of the Thames and South of the Humber River; West Saxon lay south and southwest of the Thames; and the smallest, Kentish region lay southeast of the Thames, a small corner of England. The Kentish region, settled by the Jutes from Jutland, has the scantiest literary remains.
Was it always known as old english?
Old English (Ænglisc, Anglisc, Englisc) or Anglo-Saxon 