Isidore of Seville

Isidore wrote the Etymologies — a twenty-book encyclopaedia trying to summarise everything the late ancient world knew, from grammar and medicine to ships and furniture. It became the standard reference book for the entire Middle Ages. Every monastery in Europe had a copy. Modern people propose him as the patron saint of the internet, half-jokingly, because he was the first person to seriously attempt 'all human knowledge in one searchable system.' He also organised the Visigothic church in Spain at a moment when most of the Western empire was illiterate. Without Isidore, the centuries between Gregory the Great and Charlemagne are dramatically darker.