Augustus
Augustus' reign laid the foundations of a regime that lasted, in one form or another, for nearly fifteen hundred years through the ultimate decline of the Western Roman Empire and until the Fall of Constantinople in 1453. Both his adoptive surname, Caesar, and his title "Augustus" became the permanent titles of the rulers of the Roman Empire for fourteen centuries after his death, in use both at Old Rome and at New Rome. In many languages, "Caesar" became the word for "Emperor", as in the German "Kaiser" and in the Bulgarian and subsequently Russian "Tsar" (sometimes Csar or Czar). The cult of "Divus Augustus" continued until the state religion of the Empire was changed to Christianity in 391 by Theodosius I. Consequently, there are many excellent statues and busts of the first emperor. He had composed an account of his achievements, the "Res Gestae Divi Augusti", to be inscribed in bronze in front of his mausoleum. Copies of the text were inscribed throughout the Empire upon his death. The inscriptions in Latin featured translations in Greek beside it, and were inscribed on many public edifices, such as the temple in Ankara dubbed the "Monumentum Ancyranum", called the "queen of inscriptions" by historian Theodor Mommsen.
Julio-Claudian dynasty
Although Augustus' succession plans were all but ruined due to the deaths of more than several family members, including many of his own descendants, in the end Tiberius remained faithful to his predecessor's wishes that the next emperor would hail from the Julian side of the Imperial family. Thus, Tiberius was succeeded by Gaius Julius Caesar Augustus Germanicus, the sole-remaining son of his adopted son Germanicus. The new emperor not only belonged to both the Julian and Claudian sides of the Imperial family, but was also a direct descendant of Augustus Caesar through his mother Agrippina the Elder. More commonly remembered in history by his childhood nickname Caligula, he was the third Roman Emperor ruling from AD 37 to 41.