On its website, metmuseum.org, the Metropolitan Museum of Art in New York offers a comprehensive list of Roman emperors. This list offers the years ruled of each emperor and divides the succession into separate dynasties. History.com features insights and descriptions of the lives of the emperors included on the list.
In 27 B.C., the title of Roman Emperor was created for Octavian. The great-nephew and adopted son of the historic Julius Caesar, Octavian completed his uncle's unification of the various Roman Republic's factions and assumed the title Augustus. He ruled roughly 40 years until 14 A.D., making him the longest reigning emperor.