Dionysius Exiguus; Dionysius the Little
Monk and writer.
Much of his life was spent in Rome, where he was abbot of a monastery.
He translated standard works from Greek into Latin and the beginnings of canon law in Western Christendom are due to him.
In a work on the calculation of Easter he introduced the use of the Christian Era fixing the date of Our Lord's birth as 753 years after the foundation of Rome, a date now known to be too late by four to seven years.
His surname, "the Little," is believed to have been adopted in self-depreciation.
New Catholic Dictionary