As Augustus's central role in the principate solidified, it became increasingly important for him to designate an heir. He first adopted his daughter Julia's three sons by Marcus Agrippa, renaming them Gaius Caesar, Lucius Caesar and Marcus Julius Caesar Agrippa Postumus. After the former two died young and the latter was exiled, Augustus adopted his stepson Tiberius Claudius Nero on condition that he adopt his own nephew, Germanicus (who was also Augustus's great nephew by blood). Tiberius succeeded Augustus and on Tiberius's death Germanicus's son Caligula became emperor.