Doku (ドーク重鬼卿 Do-o-ku Ju Ki Kyou, Heavy Demon Lord, Doku) is a villain from Ninja Gaiden and Ninja Gaiden Sigma, he is the Lord of the Greater Fiends of the Vigoor Empire, and Ryu Hayabusa's main antagonist throughout the early to mid-late portions, as the instigator who set off a chain of events affecting Ryu.