The great Enrico Caruso taking us through the vowels as shown in Caruso's Method of Voice Production: the Scientific Culture of the Voice (1922) by Pasqual Mario Marafioti. When he died in 1921 Caruso left behind him approximately 290 commercially released recordings, and a significant mark upon on the opera world including more than 800 appearances at the New York Met. He is considered by many to be truly the world's first popstar.
You can listen to some of the music itself and read more about Caruso in John Potter's article over at The Public Domain Review.
Photos taken from Caruso's Method of Voice Production: the Scientific Culture of the Voice (1922) by Pasqual Mario Marafioti, housed at the Internet Archive and donated by the University of Toronto