The answer to the first question is easy: Caccini was a sixteenth-century composer, based in Florence, and a gifted singer in his own right. To answer the second question, though, is to approach something of a minefield.
No one really knows who wrote this Ave Maria – mainly because the setting didn’t come to light until the twentieth century. Although its presence on any classical crossover singer’s album is now almost guaranteed, the piece was unknown before the 1970s. One plausible reason as to why this might be is that this Ave Maria arguably wasn’t composed until then. Many argue that its creator was, in fact, one Vladimir Vavilov, a relatively unknown Russian guitarist and composer, who recorded it in 1972 and declared it to be an anonymous song. The attribution to Caccini was then supposedly made at a later date by a musician who performed with Vavilov.
Whatever the truth, it’s certain that this simple melody is beloved by many. The Lithuanian soprano Inessa Galante was the singer who captivated our hearts with her performance of it in the 1990s, and it remains a firm favourite today
Read more at http://www.classicfm.com/composers/giulio-caccini/music/ave-maria/#0mU9T69UYBVzjrXR.99