Orso Ipato (Latin Ursus) was the third traditional Doge of Venice (726–737) and the first historically known. Sometime in the early 8th century, he was elected to lead the Venetians and granted the title of dux, which has morphed in the Venetian dialect into doge. He was not a duke.
Orso himself came from Heraclea. He was eventually recognised by the Byzantine Emperor Leo III the Isaurian, who gave him the title hypatos. His descendants surnamed themselves Ipato on the basis of this imperial honorific. The Orseolo family was also descended from him. After Orso's violent death (assassinated perhaps at the instigation of Eutychius, Exarch of Ravenna), there was an interregnum filled by four magistri militum before his son, Teodato, was elected as the second historical doge of Venice.
Dominicus Leonus as magister militum per Venetiae