Sejanus is one of the King of Attolia's attendants in The King of Attolia. He is famous for his pranks on the king and other people. He is the younger son of Baron Erondites and younger brother of Dite. The name and character are likely inspired by the Roman Sejanus].
As Baron Erondites's younger son, Sejanus appears to support most of his father's schemes and appears to dislike his brother immensely. Since Dite has opposed his father by supporting the queen of Attolia, Sejanus has been favoured and supported by their father.
Previously a lieutenant in the Queen's Guard, Sejanus is assigned to become one of the king's attendants because of his father's power. While he appears cheerful and capable, he holds a great deal of contempt for the new king and manipulates all of the king's attendants so that the king will appear foolish. Because Eugenides does not oppose their cruel tricks, Sejanus believes that he has made himself indispensable to the the king and that he cannot be punished.
When Eugenides learns of the schemes of the House Erondites to undermine the crown by forcing him to purge his current attendants, save Sejanus, and replace them with supporters of Erondites, the king is able to finish formulating a plan to destroy the Erondites. He forces Sejanus to confess before his other attendants for attempting to poison the king, and then implicates Dite into the crime as well. Though neither were involved, the confession is sufficient to force Sejanus to comply and allow himself to be arrested for punishment. Sejanus had despised the king and had been jealous for his brother, who had been an unsuccessful suitor to the queen, and willing accepts his fate in hopes that Dite will not suffer painfully in exile.
While imprisoned, Sejanus is unaware of his brother's exile to Ferria, save a possible letter that Dite attempts to send to him before he leaves Attolia.