The life of Dionysius Exiguus (Dennis the Little) stretched across the fifth and sixth centuries. He was a monk in a land that is today part of Romania. Dionysius was renowned for his humility, which is where the “Little” moniker comes from, and which is why you probably don’t know his name. But I’ll bet you’ve used his technology, and unless you’re a scholar working in a multi-religious environment you’re probably using it still. (Pluralists favor “C.E.” for “Common Era.”)
Dionysius liked to calculate calendars. He was the go-to guy for figuring out the date of Easter. But he’s best known for inventing the term “Anno Domini” (A.D.) — “The Year of the Lord” — to differentiate the years after the Incarnation from the years before. So you might say he had a big impact on history, for such a little guy.
Roger Pearse points us to the first English translation of Dionysius’ most important work. It’s only partial, but it’s free and posted on a Russian site. Roger’s thinking about finishing the job in his spare time.