[this paper is now available only in my book, The One-Minute Apologist]
Heinrich Bullinger (1504-1575; prominent early Protestant leader and author of the Second Helvetic Confession):
What pre-eminence in the eyes of God the Virgin Mary had on account of her piety, her faith, her purity, her saintliness and all her virtues, so that she can hardly be compared with any of the other saints, but should by rights be rather elevated above all of them, appears very clearly in the first chapters of the gospels of St. Matthew and St. Luke, and particularly in her Magnificat . . . If Mary really is the Mother of the Lord, . . . then it is altogether just that she should be named by the Fathers of the Church theotokos, that is to say Mother of God. Nestorius denied that in the most infamous manner . . .
(in Max Thurian, Mary: Mother of all Christians, translated by Neville B. Cryer, New York: Herder & Herder, 1963, 197-198; 89; from Uber die Selige Jungfrau, May 18, 1558)