Ecclesiastical Chronicle, Volume 1

This last point is something Barhebræus himself reproaches him for: "Eutyches," he says1, "introduced an alien dogma, asserting that God the Word did not assume a body from the Virgin, but just as air is incorporated by cold to become snow or rain, so he was incarnated." To instill his heresy more easily, Eutyches said2: "I confess the Lord our God was OF TWO NATURES before the union; but after the union, I confess ONE NATURE." But this was no less worthy of reproach, "since," as St. Leo observes, "it is as impious to say that the only-begotten Son of God was of two natures before the incarnation, as it is wicked to assert a singular nature in him after the Word was made flesh."

Leaders of Monophysitism: Dioscorus;

Dioscorus, the Patriarch of Alexandria, who played a leading role in the Robber Council of Ephesus, passed the error of Eutyches to the Egyptians.
Barsumas;

To the Syrians, and then to the Armenians through his disciple Samuel, it was passed by Barsumas the archimandrite, who held a place in that same assembly of monks of the whole East. Once Eutyches, Dioscorus, and Barsumas were condemned by the Council of Chalcedon, their followers were called by the Greek word Monophysites, or assertors of one nature. Soon, as is characteristic of error, they were divided into various sects that anathematized one another. All those sects agreed in this: they denied two natures in Christ and admitted only one. But while the Eutychians asserted the body of Christ was incorruptible, the Severians asserted it was corruptible and passible, the Theopaschites attributed passions to the divinity, and others taught other things. Those Syrians, however, who were later called Jacobites, were led by...

1: Infra p. 160.
2: Epist. XXVIII S. Leonis ad Flavian., Patrol. lat., LIV, 777.