According to the Internet source given below, Magister Zacharias (known variously as [Antonius Zachara da Teramo, Zacar, Zachara und Zacharias, Zaccara, Zeltenpferd ?? and Magister Zacharias Chantor Domini nostri Pape) was an Italian Papal singer active in the late 14th century.
He wrote motets, including Sumite carissimi, and secular pieces. He is listed in the Roman papal lists between 1391 and 1407 as scriptor litterarum apostolicarum and cantor.

Websites:
	Magister Zacharias	Brief biography by www.hoasm.org