The giant in Norse mythology associated with chaos and predicted to play a significant role during Ragnarok is Fenrir, the monstrous wolf. Fenrir is prophesied to unleash devastation upon the gods, signifying betrayal and destruction during this apocalyptic event. His existence underscores themes of fear, inevitability, and the conflict between chaos and order in the mythology, reflecting the cyclic nature of existence where destruction paves the way for renewal.