Aistulf (†756) was Duke of Friuli from 744, and King of the Lombards from 749 until his death in 756. He attacked the Byzantine dominions repeatedly, including Ravenna and Rome.
Venice started as a Byzantine duchy, ruled by a “dux”, but at some point, they started choosing their own dux — or doge. When, or even who, is not clear.
The Kingdom of the Lombards played a major role in early Venetian history, as it was the Lombard invasion of Italy in 568 which started the formation of later Venice.