Augustus the first emperor of Rome adopts his step-son Tiberius ensuring the hereditary succession of the principate.
Tiberius would rule the Empire from AD 14 to AD 37, and was already quite old when he finally took over the running of the Empire. Tiberius was certainly not Augustus’ first choice to take over the principate but the deaths of Caius and Lucius Caesar, and Marcus Agrippa left him little choice. As part of Augustus’ adoption of Tiberius, he was required to adopt his nephew Germanicus.
Tiberius was a great general in his own right, prior to the adoption, and had faithfully served the state for the majority of his life, but he is likely most remembered for his retirement to Capri in AD 26 which allowed the Praetorian Prefect Sejanus to exercise undue authority.
Sejanus began a series of maiestas (treason) trials ridding himself of senators and wealthy citizens that might have opposed him. In the end it appears that Sejanus planned to kill Tiberius.
Tiberius discovered the plot and had the Senate call Sejanus where a letter by Tiberius was read aloud condemning the Praetorian Prefect who was tried convicted and executed within a week.