Who is El Maestro in the book, The Magic Strings of Frankie Presto?

El Maestro is Frankie's guitar instructor and secretly his father. A blind and cantankerous drunk, El Maestro is nevertheless a brilliant and passionate guitar player. He was once the most promising musician in Spain until he was wounded in a war while saving his wife's brother. Burdened by tragedy, El Maestro believes his wife and unborn child died during a raid on a church. He never finds out that his wife managed to give birth and that his pupil, Frankie, is truly his son.