The surname Fothergill has gone through many such changes. In England it can be found as Futhergill, Fuddergill, Fuydergyle, ffothergill, de Fothergill, and Fodyrgyll. The American branch had variations of the spelling such as Firthergill, Fathergale, Firthirgal, Furthingale, Furthirgale, and Ferdigal. With the large mixture of cultures and speech patterns, and the use of phonetic spelling, the surname Fothergill has taken some abuse. It's worth mentioning that these variations weren't used by members of the family but were rather misspellings on the part of others.
Chances are that the present spelling is a relatively accurate compromise on the original.
He also reminds us that the Vikings were great sea-farers and spread throughout the northern part of Europe, including Normandy. Fothergill points to evidence that William the Conqueror was of Viking origin and ties this to the origins of the Fothergill family in Great Britain. A Sir George Fothergill was a general in Duke William's army. He was known as one of the greatest commoners in York, and as a great commander. He married Isabel, the sole daughter and heiress of William le Lucy of Folton and had five sons, all of whom were prominent in England.