Languages are not "founded" as such. What English is at its origin is the branch of the North Sea Germanic (Ingvaeonic) language family which slowly established itself in Britain during the Migration Period, as it displaced native Brythonic languages there.

From a mythohistorical standpoint (i.e., the sort of perspective wherein we do treat languages and peoples as having been "founded"), an invasion narrative places the Anglo-Saxon settlement of Britain in the mid-5th century, and attributes it to two brothers, Hengist and Horsa. These are the Romulus and Remus of England, but as such, are not to be taken as historical personages, nor should their deeds be treated as historical events. This is simply the ethnolinguistic foundation myth. Nonetheless, it is an influential one, recalled by Early Medieval historians addressing the period.

Old English, the earliest phase of English, is not intelligible with Modern English, and is more closely intelligible with the Frisian and (to a lesser extent, as it has changed much itself) Low Saxon languages of Denmark, Germany, and the Netherlands. To that extent, the language has changed dramatically, in the past 1500 years.