 Although he was the second person named Otto in the Hachberg-Sausenberg line of the House of Zähringen, he is consistently called Otto III in the literature, because he was the third bishop of Constance named Otto.Otto was the eldest son of Margrave Rudolf III of Hachberg-Sausenberg and his second wife, Anne of Freiburg-Neuchâtel.Already in 1403, when he was just 15 years old, he was mentioned as a canon in Basel.