Which Byzantine emperor signed the Union of Lyons in 1274 to reunite with the Catholic Church?

Michael VIII Palaiologos agreed to the Union of Lyons in 1274, seeking to reunite the Byzantine and Catholic Churches.

The agreement was reached at the Second Council of Lyon, where Byzantine representatives presented letters from Michael VIII, his son Andronikos, and the Byzantine clergy. The Byzantine side accepted key Western positions, including papal primacy and the use of the Filioque clause in the Nicene Creed. The union was formally proclaimed during the council.

Michael’s decision was driven largely by politics as well as religion. Constantinople had been recovered from the Latin Empire only in 1261, and Michael feared a new Western attack led by Charles of Anjou. Union with Rome could remove papal support for his enemies and potentially secure military assistance against threats to the restored empire.

The agreement never became a lasting reconciliation. Many Byzantine clergy and citizens opposed it, and Michael’s son and successor, Andronikos II, repudiated the union after Michael’s death. Thus, Michael VIII is the canonical answer even though envoys represented him at Lyon rather than the emperor personally attending.