Albanactus was the legendary founding king of Albany as accounted by Geoffrey of Monmouth. He was the youngest son of Brutus and a descendent of Aeneas of Troy. Upon his father's death, he was given the area of Albany, named after him, in Britain which corresponds roughly to present-day Scotland. This was before the Picts and Scots had invaded.

According to legend, Albanactus was killed shortly after he began his reign by Humber, who was king of the Huns. Humber invaded Albany from Germany and met Albanactus's army in battle, where Humber killed Albanactus. This forced the people of Albany to flee south to Albanactus's brother, Locrinus. Following his death, Albany seems to have been divided among Locrinus and Kamber, his other brother.