Primogeniture is notably absent in the history of the Julio-Claudian dynasty. Neither Augustus, Caligula, nor Nero fathered a natural and legitimate son. Tiberius' own son, Drusus predeceased him. Only Claudius was outlived by his son, Britannicus, although he opted to promote his adopted son Nero as his successor to the throne. Adoption ultimately became a tool that most Julio-Claudian emperors utilized in order to promote their chosen heir to the front of the succession. Augustus—himself an adopted son of his great-uncle, the Roman dictator Julius Caesar—adopted his stepson Tiberius as his son and heir. Tiberius was, in turn, required to adopt his nephew Germanicus, the father of Caligula and brother of Claudius. Caligula adopted his cousin Tiberius Gemellus (grandson of the emperor Tiberius) shortly before executing him. Claudius adopted his great-nephew and stepson Nero, who, lacking a natural or adopted son of his own, ended the reign of the Julio-Claudian dynasty with his fall from power and subsequent suicide.