Alexius III (1338-1390), was Grand Comnenus and Emperor of Trebizond from 1349 until his death. He was son of Emperor Basil and his second (and bigamous) wife, Irene.

When his father died and his first wife Irene Palaeologina succeeded him, she sent all the children of her dead husband to Constantinople and young John (because that was his real name) raised at the Byzantine court. When he was twelve he had been sent to Trebizond by John VI Cantacuzenus to depose his great-uncle Michael who was an instrument of the regency Cantazuzenus had displaced. Without any troubles he assumed the throne and took the name of Alexius, the name of his deceased brother who had accompanied him but died prematurely, because of its better connotation with the people of Trebizond. Two years later, in 1351 Alexius was married to John's niece, Theodora Cantacuzena, in the newly rebuilt Church of St. Eugenios. For the time, Alexius was accepted as Emperor because of his youth, which proved acceptable to the nobles of the realm who sought to use young ruler's regency for their own purposes.

Alexius III of Trebizond and Theodora Cantacuzena

However, young Emperor with the help of his mother and loyal generals put an end to civil war, defeating Nicetas, the kingmaker, and rebellious nobles. In 1355 Kenchrina, the last fortress resisting Alexius was captured an the fifteen years civil war was finally at an end. He did not succeed however in regaining lost territory or restoring to the imperial institution the previous respect and power. In particular, Alexius was unable to suppress the ambitions of the landed aristocracy which developed during the civil war or to displace the Genoans and Venetians from their dominance in Trebizond's commerce.

Alexius repaired the physical damage to the capital, gave rich endowments to several monasteries, especially Sumela Monastery, and founded the Dionysiou Monastery at Mount Athos. The typikon of the Dionysiou is an object of artistic merit and beauty.

He and his wife had six children:

Basil Comnenus (1358 - 1377),

Manuel III (1364 - 1417), Emperor 1390 - 1416,

Eudocia, married first to Tajaddin, Emir of Limnia and then to Constantine of Serbia,

Maria, married Suleiman Beg, Emir of Chalybia,

NN, married Mutakharten, Emir of Arsinga,

Anna, married King Bagrat V of Georgia,

Alexius had also at least two illegitimate sons: John and Andronicus (1355 - 1376), who married Gulkhan-Eudocia, daughter of King David IX of Georgia, but he was murdered shortly after and Eudocia married his brother, Manuel.

The sisters of the Emperor, Maria and Theodora, were both married to Koutlobeg the chieftain of the White Sheep and the Emir of Chalybia respectively. Many Byzantines were shocked by his willingness to give his daughters to Muslim princes in order to give his country protection without returning it territories. In this respect, Alexios also diminished part of his country's dignity.

When Alexius III died in 1390 his son, Manuel III, succeeded him.

Preceded by: Michael
Emperor of Trebizond 1349 — 1390
Succeeded by: Manuel III