Sejanus

Sejanus commands the Praetorian Guard and stands close to the throne, a soldier of low birth who has made himself indispensable to Tiberius. He is composed, watchful, and relentlessly capable, the sort of man who solves problems before anyone notices they existed. Ambition sits just under his calm surface, patient and unhurried.

Stewart plays him with a stillness that reads as total control, a man who never raises his voice because he has never needed to. The scripts give Sejanus real competence rather than mere villainy, so his rise looks earned, even reasonable, which makes him far more unsettling than a simple schemer would be.