John V Palaiologos or Palaeologus (Greek: Ἰωάννης Παλαιολόγος, romanized: Iōánnēs Palaiológos; 18 June 1332 – 16 February 1391) was Byzantine emperor from 1341 to 1391, with interruptions. His long reign was marked by constant civil war, the spread of the Black Death and several military defeats to the Ottoman Turks, who rose as the dominant power of the region.
John V became emperor at age eight, which resulted in a civil war between his regent John VI Kantakouzenos and a rival council led by his mother Anna of Savoy, who pawned the crown jewels to Venice in order to raise funds. Kantakouzenos was recognized as emperor in 1347, coinciding with the arrival of the Black Death. Shortly after, another civil war erupted in 1352, with John V seeking help from Serbia against John VI's son Matthew and his enlisted Ottoman Turks. The Turks used the ensuing chaos to gain their first European territory on former Byzantine soil.