from Wikipedia:
Lucius Aelius Sejanus
20 BC – 31
Roman As depicting Tiberius, struck in 31, Augusta Bilbilis. The reverse reads Augusta Bilbilis Ti(berius) Caesare L(ucius) Aelio Seiano, marking the consulship of Sejanus in that year.
Place of birth
Volsinii, Etruria
Place of death
Rome
Allegiance
Roman Empire
Years of service
14 BC – 31
Rank
Praetorian prefect
Commands held
Praetorian Guard
Other work
Consul of the Roman Empire in 31
Lucius Aelius Seianus (20 BC – October 18, 31 AD), 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 14 AD until his death in 31.
While the Praetorian Guard was formally established under emperor Augustus, Sejanus introduced a number of reforms which saw the unit evolve beyond a mere bodyguard into a powerful and influential branch of the government involved in public security, civil administration, and ultimately political intercession; changes which would have a lasting impact on the course of the Principate.
During the 20s, Sejanus gradually accumulated power by consolidating his influence over Tiberius and eliminating potential political opponents, including the emperor's son, Julius Caesar Drusus. When Tiberius withdrew to Capri in 26, Sejanus was left in control of the entire state mechanism as de facto ruler of the empire. For a time the most influential and feared citizen of Rome, Sejanus suddenly fell from power the same year his career culminated with the consulship in 31. Amidst suspicions of conspiracy against the emperor, Sejanus was arrested and executed, along with his followers.