This essay is a comparison between Celtic myth and Korean myth with emphasis on hero Cuchulain and Jumong. Cuchulain is a Celtic Irish mythological hero who appears in the stories of the Ulster Cycle. In this study the main text of Cuchulain is Lady Gregory's Cuchulain of Muirthemne. Jumong, whose birth name was Dongmyeongseongwang(東明聖王), was the founding monarch of Goguryeo. The best known version of the founding myths of Goguryeo is the Dongmyeongwangpyeon of the Dongguk I Sanggukgip(Collected Works of Minister Yi of Korea) by Yi, Gyu Bo. According to Jeseph Campbell's idea of monomyth the standard path of the mythological adventure of the hero is a magnification of the formula represented in the rites of passage: separation−initiation−return. A hero ventures forth from the world of common day into a region of supernatural wonder, fabulous forces are there encountered and a decisive victory is won, and the hero comes back from this mysterious adventure with the power to bestow boons on his fellow man. Cuchulain and Jumong's hero-journey show the nuclear unit of the monomyth. Their stories exhibit with extraordinary clarity all the essential elements of the classic accomplishment of the impossible task. Cuchulain is the son of the sun god Lugh and Deichtire(a daughter of Maga, the child of the love god of Angus). Jumong is the son of Hae Mosu(解慕漱: the son of heaven) and Yuhwa(柳花:daughter of the river god Habaek(河伯). Cuchulain and Jumong are the child divine yet born of human mather. They are sons of sun and abandoned by their divine father. The characteristic adventure of Cuchulain is winning of the bride, Emma. The adventure of Jumong is going to succeed to his father-the father is the invisible founder of Buyeo. Cuchulain's adventure had given him the capacity to annihilate all opposition. At the age of seventeen Cuchulain single-handedly defends Ulster from the army of Connacht in the Tain Bo Cuailnge. Jumong's adventure had given him the capacity to rule his subjects. At the age of twenty-two, in 37 BC, Jumong established Goguryeo, and became its first "Supreme King." Goguryeo considered itself a successor to Buyeo. Cuchulain, the Irish Achilles, is the symbol of all those who fought for independence of Ireland. Jumong, the korean Achilles, is the symbol of the pride of Korean. The aim of this essay is that my comparative analysis contribute to the sense of universal understanding of the human condition.