"He is a sincere man. At least, he is not a villain. More like a government official who doesn't accept any kind of bribe--a stubborn, straight-laced man." - Dalton Strauss
Archangelo (アークアンジェロ, Ākuanjero) is one of three surviving pre-1711 immortals, along with Dalton Strauss and Renee Parmedes Branvillier. As of 1935-C there is no official art of him (though his hand is depicted resting on Renee's head).
He, along with Dalton and Renee, was a professor who taught alchemy at Lotto Valentino's Third Library in the 1700s, an education that would give Maiza Avaro and the other students the knowledge that would eventually give them the means to summon a demon in 1711. Archangelo has stated that he has forgotten "more than half of them," referring to his students.
Originally, there were ten pre-1711 immortals, including himself. However, Archangelo is the reason that Dalton, Renee and himself are the only survivors. He devoured an unknown number of the other seven immortals for the sake of 'protecting Renee'--through his actions, he was reducing the chance that Renee might be devoured one day. His desire to protect Renee stems from his love for her, which he knows that Renee will never realize nor reciprocate. Despite knowing this, he is immensely devoted to her and has vowed to protect her no matter what.
Renee has on at least one occasion mistaken him for Elmer based on the sound of his voice (he was talking to her through a cabin door).
Archangelo harbors feelings of intense hatred for a former student of his (Huey Laforet), due to Huey gouging out Renee's right eye in 1934. The fact that Renee is the mother of Huey's children is also a source of discomfort for him.