What is "hucbald"

Hucbald (Hucbaldus, Hubaldus) (c. 840 or 850 – June 20, 930) was a Frankish music theorist, composer, teacher, writer, hagiographer, and Benedictine monk. Deeply influenced by Boethius' De Institutione Musica, he wrote the first systematic work on western music theory, aiming at reconciling through many notated examples ancient Greek music theory and the contemporary practice of the more recent so-called 'Gregorian chant'.