Isaac of the Caves was an 11th-century monk and hermit who lived at the Kyiv Pechesk Lavra. Originally a wealthy merchant named Chern, he renounced his possessions to join the monastery under Saint Anthony. After spending seven years in seclusion, he experienced a profound spiritual trial involving a deceptive vision, which led him to embrace the life of a holy fool. He died around 1090 and is recognized as a saint in both Eastern Orthodox and Catholic traditions.