Instead, he insisted on imposing Roman rites on the Celts, a move which was not only contrary to Gregory's advice, but established the first fissure in the eventual breach between the Church of Rome and what would become, centuries later, the Church of England and, eventually still, The Episcopal Church of the United States. [Although, to be historically accurate, the Episcopal Church owes its identity not to the Church of England as much as it does the Scottish Episcopal Church, bishops of which consecrated the first bishop of the American church. It's from the Scots that we get our name, too.]
More can be read of him at this site.
[Above is a photo of the first parish I ever served as vicar/rector: St. Augustine of Canterbury in Edinboro, Pennsylvania.]