Gregory is remembered for two things beyond his administration: a mission and a method. Bede's Ecclesiastical History of the English People tells the story, probably improved in the telling, that Gregory saw fair-haired boys for sale in the Roman slave market, was told they were Angles, and replied that they were not Angles but angels, and resolved to send missionaries to convert their homeland. Around 596 he dispatched a monk named Augustine, prior of his own monastery on the Caelian Hill, at the head of about forty companions to Kent, where King Aethelberht permitted them to preach.
Augustine became the first Archbishop of Canterbury, and the mission is conventionally credited with beginning the conversion of Anglo-Saxon England to Christianity, though older British Christianity had survived in the west of the island independently. Gregory's other lasting legacy is the Regula Pastoralis, a handbook on the duties and temptations of bishops that he wrote near the start of his pontificate, which circulated so widely in the medieval West that Alfred the Great later had it translated into Old English for his own clergy, and the Byzantine emperor Maurice had it rendered into Greek in Gregory's own lifetime. He also completed the Moralia in Job, a vast allegorical commentary begun during his years in Constantinople, and later tradition, though not history that can be verified, credited him with organizing the corpus of liturgical chant that still bears his name as Gregorian chant. He died in Rome in 604 and was acclaimed a saint immediately, one of the four original Doctors of the Latin Church.