Venerable Hilarion was a strict ascetic and a disciple and co-ascetic with Saint Theodosius (May 3) in the Far Caves of the Kiev Caves Lavra. Hilarion is said to have kept such abstinence that he ate very little once a week, and as a cohabitant of Saint Theodosius he imitated him by praying day and night with prostrations and tears, pleasing God.
His contemporaries knew him as a chronicler, who toiled over the copying of books in the cell of Saint Theodosius day and night. During this time his teacher would chant Psalms softly and spin wool or do something else. We are informed of his great temptations from demons, and how Venerable Theodosius often exhorted him to endure these temptations and with his prayers delivered him from them.
Saint Hilarion reposed in the late eleventh century and his incorrupt relics rest in the Far Caves. He is sometimes confused with Metropolitan Hilarion of Kiev.