Lucius Aelius Sejanus (20 BC-AD 31) was a Roman army officer who rose to become commander of the Praetorian Guard under the Emperor Tiberius, and virtual ruler of the Roman Empire after Tiberius retired to Capri. When Tiberius discovered his plotting he had Sejanus and his supporters brutally murdered.
Sejanus was notably portrayed by Patrick Stewart (of later Star Trek fame) in the BBC's 1976 adaptation of the novel I, Claudius by Robert Graves.