Theodo or Theoto (about 625 – 11 December c. 716), sometimes numbered Theodo II, was the Duke of Bavaria from 670 or, more probably, 680 to his death. It is with Theodo that the well-sourced history of Bavaria begins. He strengthened his duchy internally and externally and, according to the medieval chronicler Arbeo of Freising, he was a prince of great power whose fame extended beyond his borders.
Saint Emmeram of Regensburg (also Emeram(m)us, Emmeran, Emmerano, Emeran, Heimrammi, Haimeran, or Heimeran) was a Christian bishop and a martyr born in Poitiers, Aquitaine. Having heard of idolatry in Bavaria, Emmeram travelled to Ratisbon (Regensburg) some time after the year 649 to the court of Theodo I, Duke of Bavaria. He supposedly travelled up the Loire, crossed through the Black Forest and then followed the Danube to Regensburg. Theodo welcomed Emmeram to his court, where he laboured for three years carrying out missionary work. During this time, he gained a reputation as a pious man. He died circa 652 and is buried in St. Emmeram's in Regensburg, Germany. His feast day in the Catholic Calendar of saints is September 22.