High Quality Content by WIKIPEDIA articles! Lucius Aelius Seianus (20 BC – October 18, AD 31), commonly known as Sejanus, was an ambitious soldier, friend and confidant of the Roman Emperor Tiberius. An equestrian by birth, Sejanus rose to power as prefect of the Roman imperial bodyguard, known as the Praetorian Guard, of which he was commander from AD 14 until his death in 31.