Catherine Zaccaria in the context of "Despot of the Morea"

Thomas Palaiologos (Greek: Θωμᾶς Παλαιολόγος; 1409 – 12 May 1465) was Despot of the Morea from 1428 until the fall of the despotate in 1460, although he continued to claim the title until his death five years later. He was the younger brother of Constantine XI Palaiologos, the final Byzantine emperor. Thomas was appointed as Despot of the Morea by his oldest brother, Emperor John VIII Palaiologos, in 1428, joining his two brothers and other despots Theodore and Constantine, already governing the Morea. Though Theodore proved reluctant to cooperate with his brothers, Thomas and Constantine successfully worked to strengthen the despotate and expand its borders. In 1432, Thomas brought the remaining territories of the Latin Principality of Achaea, established during the Fourth Crusade more than two hundred years earlier, into Byzantine hands by marrying Catherine Zaccaria, heiress to the principality.

In 1449, Thomas supported the ascension of his brother Constantine, who then became Emperor Constantine XI, to the throne despite the machinations of his other brother, Demetrios, who himself desired the throne. After Constantine's rise to the throne, Demetrios was then assigned by Constantine to govern the Morea with Thomas but the two brothers found it difficult to cooperate, often quarreling with each other. In the aftermath of the Fall of Constantinople and end of the Byzantine Empire in 1453, Ottoman Sultan Mehmed II allowed Thomas and Demetrios to continue to rule as Ottoman vassals in the Morea. Thomas hoped to turn the small despotate into a rallying point of a campaign to restore the empire, hoping to gain support from the Papacy and Western Europe. Constant quarreling with Demetrios, who supported the Ottomans instead, eventually led Mehmed to invade and conquer the Morea in 1460.