Tavius was a high-ranking member of Emperor Nero's court in Rome. Secretly a Christian, he agreed to assist Maximus Pettulian in his plot to kill Nero.
He tried to purchase Barbara Wright as a slave after seeing her concern for a fellow slave, but was told he could only bid for her at the slave auction. At the auction he bid ten thousand sestertia for her and took her back to Nero's palace to serve the Empress Poppaea.
Tavius met with the First Doctor, who he believed was Pettulian. He discussed his plans with the Doctor, to the Doctor's confusion.
Poppaea, jealous of Barbara, ordered Tavius to dismiss her. Tavius saw this as an opportunity to help Barbara escape. On Barbara's information, he warned the Doctor that Nero wanted to make him fight in the arena.
He encountered Ian Chesterton in the palace and helped him reunite with Barbara, then helped them escape. (TV: The Romans)