Saint Ambrose [Aurelius Ambrosius] (c. 340–397), better known in English as Ambrose, was a Archbishop of Milan who became one of the most influential ecclesiastical figures of the 4th century. He was the Roman governor of Liguria and Emilia, headquartered in Milan, before being made bishop of Milan by popular acclamation in 374. Ambrose was a staunch opponent of Arianism.
Ambrose was one of the four original Doctors of the Church, and is the patron saint of Milan. He is notable for his influence on Augustine of Hippo.
Traditionally, St. Ambrose is credited with promoting "antiphonal chant", a style of chanting in which one side of the choir responds alternately to the other, as well as with composing Veni redemptor gentium, an Advent hymn. Ambrose is traditionally credited but not actually known to have composed any of the repertory of Ambrosian chant also known simply as "antiphonal chant", a method of chanting where one side of the choir alternately responds to the other. (The later pope Gregory I the Great is not known to have composed any Gregorian chant, the plainsong or "Romish chant".) However, Ambrosian chant was named in his honor due to his contributions to the music of the Church; he is credited with introducing hymnody from the Eastern Church into the West.