João Caeiro (also spelled as João Cayeyro,[1] Joano Cayeyro,[2] John Cayero[3]) was a 16th-century Portuguese mercenary in the service of King Tabinshwehti of the Toungoo Dynasty, rulers in modern day Burma (Myanmar).
He was the leader of a group of 700 Portuguese mercenaries who as musketeers and artillery men fought at the battle of Martaban (1540–41).
They were opposed by Martaban's defenses which employed another group of Portuguese mercenaries led Paulo de Seixas.
Caeiro is said to have seriously considered defecting to the side of Saw Binnya, the ruler of Martaban, who had offered him an enormous bribe.
He rejected the offer after his Portuguese officers threatened to report the matter to the Burmese king.