Chief administrator of the Roman Empire for the emperor Tiberius alleged murderer of Tiberius´ only son Drusus Caesar and suspect in a plot to overthrow Tiberius and become emperor himself.
Sejanus was related through his mother to the distinguished senatorial family Cornelii Lentuli.
In 14 upon the accession of Tiberius he joined his father Seius Strabo as prefect of the Emperor´s household troops the Praetorian Guard and became sole prefect a year or two later.
After the death of Drusus in 23 he began systematically to attack the position of Drusus´ mother Vipsania Agrippina (the elder) whose sons were Tiberius´ probable heirs.
In 25 he was refused Tiberius´ permission to marry Drusus´ widow Livilla who may have been Sejanus´ accomplice in the poisoning of her husband.
The next year Sejanus persuaded the Emperor to take up residence on Capreae (Capri) and in 29 succeeded in having Agrippina and her son Nero exiled.
As consul in 31 with the prospect of attaining the great administrative prerogatives of tribunicial power he suddenly fell under the suspicion of the Emperor.
Tiberius, apparently warned by his sister-in-law Antonia of Sejanus´ designs, had him arrested and executed.