Sejanus ( Lucius Aelius Seianus 20 BC -- October 18 , AD 31 ) , was an ambitious soldier , friend and confidant of the Roman Emperor Tiberius . 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 .