You can read his biography on Wikipedia. I wanted to answer the question: why Sagreras? Well, he dedicated his life to teaching. His repertoire ranges from never touching a guitar in your lfie to concert pieces. As of 2025, I went through the first 2 parts of his School of Guitar and I would advise anybody who's starting guitar to go through it. His method includes various techniques, harmonies, and they're not just exercises, but at times actual compositions. Sagreras' book teaches every aspect of guitar playing, so if you're a beginner - or even an intermediate player - I (and my teacher) would highly recommend going though it.