Justin II (15 November 565 - 5 October 578). Flavius Iustinus Iunior was emperor of the Byzantine Empire who lost most of Italy and many other territories during his reign. He became mentally ill in 574 and was forced to appoint Tiberius, Count of the Excubitors, as Caesar and regent. Empress Sophia, his wife, exerted political influence throughout his reign including the time of Tiberius' regency.