The identity of Three Initiates has been the subject of much secrecy and rumor since The Kybalion first appeared at the beginning of the twentieth century. These students were tutored by Hermes Trismegistus (the father of the occult, the founder of astrology, the discoverer of alchemy) on his supposed understanding of the universe and our relationship with it.
The Kybalion: Hermetic Philosophy is a 1908 book claiming to be the essence of the teachings of Hermes Trismegistus, published anonymously by a group or person under the pseudonym of "the Three Initiates". (Introduction by Wikipedia)