Flavius Zeno (c. 425–491), original name Tarasicodissa or Trascalissaeus, Eastern Roman Emperor (February 9 474 - April 9 491) was one of the more prominent of the early Byzantine emperors. Domestic revolts and religious dissension plagued his reign which nevertheless succeeded to some extent in foreign issues. He presided over the official end of the Roman Empire in the west under Julius Nepos and Romulus Augustus, while at the same time contributing much to stabilizing the empire in the east.

Tarasicodissa, as he was known as a young man, was an Isaurian, a people who lived on the Mediterranean coast of Anatolia, in what is now Antalya. The Isaurians, like most borderland tribes, were looked upon as barbarians by the Romans even though they had been Roman citizens for more than two centuries. Still, a fortuitous turn of events ultimately placed Tarasicodissa on the throne in Constantinople.

Well-known as a warrior, Tarasicodissa caught the eye of the Emperor Leo I in the mid-460s, when Leo was searching for alternatives to using increasingly unreliable Germanic and Alan mercenaries in his army. In 466, Tarasicodissa exposed the treachery of Ardabur, the son of the Alans eastern magister militum Aspar and made himself even more indispensable. By 468, when Leo's incompetent (and perhaps traitorous) generals led the Byzantine fleet to disaster in a campaign against the Vandals, Tarasicodissa was considered Leo's best general. While on a campaign in Thrace he narrowly escaped assassination instigated by Aspar. On Tarasicodissa's return to the capital, Aspar was killed on Leo's orders and Tarasicodissa became magister militum in his own right.

To make himself more acceptable to the Roman hierarchy and the native Greek population of Constantinople, Tarasicodissa adopted the Greek name of Zeno and used it for the rest of his life after his marriage to Leo's daughter Ariadne in 468. Although designed by Leo to secure Isaurian support against the aforementioned ambitious minister Aspar, this political arrangement brought them a son, who was to become the emperor Leo II upon the death of his grandfather in 474.

In the meantime, Zeno continued to lead the eastern armies with a great deal of success, most notably in expelling the Vandals from Epirus, which they invaded in 469 as part of King Geiseric's revenge for being attacked a year earlier. He also led troops against incursions by the Huns and Gepids south of the Danube River. Since Leo II was too young to rule himself, Ariadne and her mother Verina prevailed upon Leo to crown Zeno as co-emperor, which he did on February 9, 474. When Leo became ill and died on November 17, Zeno became sole emperor.

Zeno continued to be unpopular with the people and senate because of his "foreign" origins. A revolt fomented by Verina in favour of her brother Basiliscus in January of 475 and the antipathy to his Isaurian soldiers and administrators in Constantinople forced him to flee the capital for the city of Antioch. Zeno was compelled to shut himself up in a fortress and spent the next 20 months raising an army, largely made up of fellow Isaurians, and marched on Constantinople in August 476. The growing misgovernment and unpopularity of Basiliscus ultimately enabled Zeno to re-enter Constantinople unopposed in 476 after an army led by the general Illus defected to Zeno. His rival was banished to Phrygia, where he soon afterwards died.

Restored to rule of the Eastern Empire, Zeno was within two months forced to make a momentous decision when Romulus Augustulus was deposed by the Chieftain of the Heruli, Odovacar. Odovacar sent a deputation from the Western senate to Constantinople, where they laid the western insignia of rule before Zeno's feet. "The West, they said, no longer required an Emperor of its own: one monarch sufficed for the world; Odoacer was qualified by his wisdom and courage to be the protector of their state, and upon him Zeno was entreated to confer the title of Patrician and the administration of the Italian provinces." Zeno, recognising this as a fait accompli, accepted the requests: although he made vague protestations that the Western senate should first have turned to the deposed western emperor, Julius Nepos, he formally reunited the Empire, and granted Odoacer the title of Patrician. For a time, he left the west to itself; later, when Odoacer began calling himself "King", he began to consider possible solutions to the matter.

At the same time, Zeno sent a mission to Carthage with the intent of making a permanent peace settlement with Geiseric, who was still making constant raids on eastern cities and merchant shipping. By recognizing Geiseric as an independent king and with the full extent of his conquests, Zeno was able to hammer out a peace which ended the Vandal attacks in the east, brought freedom of religion to the Catholics under Vandal rule, and lasted for more than 50 years.

Since 472 the aggressions of the two Ostrogoth leaders, Theodoric the Great, son of Theodemir, and Theodoric Strabo, had been a constant source of danger. Although Zeno at times contrived to play them off against each other, they in turn were able to profit by his dynastic rivalries. It was only by offering them pay and high command that he kept them from attacking Constantinople itself.

Zeno survived another revolt in 478, when his mother-in-law Verina attempted to kill Illus for turning against Basiliscus, her brother. The revolt was led by her son-in-law Marcian and the Ostrogoth warlord Theodoric Strabo, but Illus again proved his loyalty to Zeno by quashing the revolt. However, Illus and Zeno had a falling out by 484, and once again Zeno had to put down a bloody revolt in the east.

After Theodoric Strabo died in 481, the future Theodoric became king of the entire Ostrogoth nation and began to be a source of trouble in the Balkan peninsula. Zeno got rid of the problem in 487 by inducing him to invade Italy to fight Odoacer who allegedly supported usperes Leontius and establish his new kingdom there. This all but eliminated the German presence in the east.

Zeno died on April 9, 491, after ruling for 17 years and 2 months. Because he and Ariadne had no other children, his widow chose a favoured member of the imperial court, Anastasius, to succeed him.

Zeno is described as a lax and indolent ruler, but he seems to have husbanded the resources of the empire so as to leave it appreciably stronger at his death.

In ecclesiastical history, Zeno is associated with the Henoticon or "instrument of union", promulgated by him and signed by all the Eastern bishops, with the design of solving the monophysite controversy.

A composition of Agathias of Myrine describes Zeno playing tabula, a sort of backgammon.