Theodore Mangaphas or Mankaphas (, fl. ca. 1188–1205) was a nobleman from Philadelphia who assumed the title of Byzantine emperor twice, first during the reign of Isaac II Angelos (r. 1185–1195 and 1203–1204), and secondly after the sacking of Constantinople during the Fourth Crusade. He was given the sobriquet Morotheodoros (Μωροθεόδωρος) meaning "Theodore the Fool", by the Greek chroniclers after his repeated failed usurpations.