One of the most popular "St. Augustines" in the English speaking world is St. Augustine of Canterbury, often called the "Apostle of the English."
Born in the 6th century, St. Augustine was handpicked by St. Gregory the Great to be one of his missionaries in distant lands.
According to the Catholic Encyclopedia, "A rumor had reached Rome that the pagan inhabitants of Britain were ready to embrace the Faith in great numbers, if only preachers could be found to instruct them."
This led St. Gregory the Great to select St. Augustine for the missionary journey.
He and his companions arrived in Britain and were greeted by King Aethelberht, who was captivated by them.
The evident sincerity of the missionaries, their single-mindedness, their courage under trial, and, above all, the disinterested character of Augustine himself and the unworldly note of his doctrine made a profound impression on the mind of the king. He asked to be instructed and his baptism was appointed to take place at Pentecost.
St. Augustine's efforts bore much fruit and Christianity took hold in Britain.
Christianity's foundation in Britain is directly connected to St. Augustine, which is why he is rightly called Apostle of the English.