From Diablo Wiki

Jump to: navigation, search

Akarat the Prophet is the name of the ascetic who founded the religion and customs of the Zakarum Church. It is said that he did so after the visit of Archangel Yaerius in his dreams.

It's highly likely he wrote the Visions of Akarat. The other possibility is that someone transcribed Akarat's visions, and helped put them in a book.