Eutyches was an archimandrite from Constantinople who started to voice complaints against Nestorius in 428. He was the spiritual father of the grand chamberlain, the eunuch Chrysaphius. In 448, a law was promulgated that forbade any Christological scheme not in accord with Nicaea or the First Council of Ephesus.
He opposed Bishop Flavian of Constantinople. Flavian censured Eutyches for having an unbalanced theology. Eutyches was condemned, appealed to Emperor Theodosius, and a council was summoned. The Second Council of Ephesus took place in 449 under the presidency of Dioscorus of Alexandria.
He restated the Cyrillian doctrine, mainly from the Twelve Anathemas, which disagreed with the Antiochene doctrine of Nestorius. Eutyches was restored and all his opponents were deposed. But Flavian died shortly after and the Pope of Rome rejected this council, calling it the robber council. After the sudden death of Theodosius in July 450, imperial officials convoked another, greater council in 451 at Chalcedon, which simply reversed the decisions of the council held in Ephesus in 449.
It is important to note that our knowledge of the Second Council of Ephesus comes mainly from the opponents of the council. The acts of this council are included in the acts of the Council of Chalcedon. Hence, it is very hard to attain a true idea of what happened. Also worthy of note is the fact that most of the attendees of this council later attended the Council of Chalcedon and changed their allegiance, claiming that Dioscorus had previously applied pressure on them.