Lucius Aelius Sejanus was an adviser of the Roman Emperor Tiberius.
He was the son of a Roman knight and had influential political connections through his mother's family. After the accession of Tiberius in 14 A.D., Sejanus and his father were made co-commanders of the Praetorian Guard. Sejanus soon became the sole commander and he acquired the complete confidence of Tiberius. He increased the power of the guard by quartering the cohorts in one camp.
As his influence over Tiberius grew, Sejanus also developed power over the Senate, particularly after the death in 23 of Drusus Caesar, the son of Tiberius. Sejanus later was implicated in the murder of Drusus. To increase his personal power, Sejanus also plotted against several other members of the imperial family and he encouraged Tiberius' decision to retire to Capri in 26.
After the Emperor's withdrawal, Sejanus' authority was unchallenged. The suspicions of Tiberius were finally aroused in 31, shortly after Sejanus had become consul, and the Emperor was convinced that his favorite was plotting to overthrow him. Sejanus was then imprisoned, condemned to death, and executed on the same day in Rome.