Final answer:
Apollinarianism was countered by the First Council of Constantinople, which upheld the doctrine that Jesus was fully man and fully God, rejecting Apollinaris of Laodicea's view of Jesus having a human body and divine mind.
Step-by-step explanation:
One of the heresies countered by the First Council of Constantinople was Apollinarianism. This heresy, proposed by Apollinaris of Laodicea, suggested that Jesus Christ had a human body and a divine mind, denying the complete dual nature of Christ as both fully human and fully divine. The Council, which took place in 381 AD, affirmed that Jesus was fully God and fully man, with a human mind and soul, thereby upholding what became Orthodox Christian doctrine.
The Council of Constantinople was one of the early ecumenical councils that aimed to establish a unified Christian doctrine and challenge various interpretations of Christianity deemed heretical. Arianism was another heresy, addressed at the earlier Council of Nicaea in 325 AD, which held that Christ was not of the same substance as God the Father, sparking significant theological debates and forming a large part of the early Christian controversies over orthodoxy and heresy.