He comes from Milan, and he is a saint because he is consecrated by the sacred church. See the related link for more information.
I was just asking this question myself and found this: http://www.saintambrogio.com/aboutus.html#Church SAINT AMBROGIO, the patron Saint of Ferentino, was a Roman soldier who was persecuted for his Christian beliefs. He refused to give up his faith and was finally slain on August 15, 304 A.D. over 1700 years ago. Nine years later when Emperor Constantine legalized Christianity by the Edict of Milan, Christians could finally openly honor their beloved Saint. A historical perspective of the Patron Saint of Ferentino can be found in the abridged translation of "la Festa in Onore di S. Ambrogio A Ferentino" by Biancamaria Valeri translated by Thomas D. Luchetti of Rockford, IL.
Emilio Ambrogio Paterno has written: 'Ambrogio Carabba archeologo e patriota'
Ambrogio Alciati has written: 'Ambrogio Alciati (1878-1929)' -- subject(s): Exhibitions
Ambrogio Pozzi has written: 'Ambrogio Pozzi' -- subject(s): Design, Exhibitions, History
Ambrogio Lorenzetti was born in 1285.
Ambrogio Casati died in 1977.
Ambrogio Casati was born in 1897.
Ambrogio Calepino died in 1510.
Ambrogio Besozzi died in 1706.
Ambrogio Besozzi was born in 1648.
Ambrogio Fogar died in 2005.
Ambrogio Fogar was born in 1941.