This name appears in the New Testament belonging to a companion of Saint Paul. He became the first bishop of Crete and was the recipient of one of Paul's epistles. This was also the praenomen of all three Roman emperors of the 1st-century Flavian dynasty, and it is the name by which the second of them is commonly known to history. Shakespeare later used it for the main character in his tragedy Titus Andronicus (1593). As an English name, Titus has been occasionally used since the Protestant Reformation.
William Shakespeare made Theseus a central character in his play A Midsummer Night's Dream (1595), about his upcoming marriage to the Amazon queen Hippolyta. Shakespeare revisited the character in his later play The Two Noble Kinsmen (1613).
As an English name, it became popular due to the Fleetwood Mac song Rhiannon (1976), especially in the United Kingdom and Australia.