Guido Aretinus

Guido Aretinus, a Benedictine monk who flourished at Arezzo, in Italy, during the 11th century, the first to promote the theoretical study of music; he is credited, amongst other things, with the invention of counterpoint, and was the first to designate notes by means of alphabetical letters, and to establish the construction of the stave.

Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)

Guicowar * Guido Reni
Guerin, Pierre
Guernsey
Guerrazzi, Francesco Domenico
Guesclin, Bertrand du
Guest, Edwin
Gueux
Guiana
Guicciardini
Guichard, Karl
Guicowar
Guido Aretinus
Guido Reni
Guienne
Guignes, Joseph de
Guildford
Guildhall
Guildhall School of Music
Guilds
Guillotine
Guinea
Guinegate