Saints are not born with halos around their heads. Cyril of Alexandria is a good example. He began his career as archbishop of Alexandria (Egypt) with impulsive often violent actions. He pillaged and closed the churches of the Novatian heretics, participated in the the desposing of St.John Chrysostom and confiscated Jewish property.

So why is he a saint? His importance for theology and Church history lies in his championing the cause of orthodoxy aginst the heresy of Nestorius. Nestorius said Mary was not the Mother of God. Cyril said she was and that Jesus her son, was truly God and truly human.