Emperor Ashtar, the self-proclaimed Emperor of Darkness, appears to be the antagonist of Ninja Gaiden II: The Dark Sword of Chaos and to have been the mastermind behind the events of the first game. He is the leader of a demonic tribe from the world of Chaos, and wields the titular Sword of Chaos, which is claimed to have been grown from the bone of the Demon.
Ashtar plans open the Gate of Darkness to the world of Chaos, thereby inheriting enough power to rule the world. This requires him to kill someone with an immortal blood which turns out to be Ryu. To achieve this, he intends first power up his Sword with souls including Irene's, and then kill Ryu to open the Gate. However he underestimates Ryu and is defeated by him.
Ashtar sends several of his tribesmen of Chaos against Ryu throughout the game. Some are created by his sorcery like Dando who is a combination of the spirits of Vikings lost at sea. Ashtar has also enhanced a lizard through science and sorcery into Funky Dynamite. Cybernatic enhancements allows this former lizard to zip through the air and attack with missiles. Other tribesmen are rejects of society picked up by Ashtar, like Baron Spider who became a half-man, half-spider through an laboratory accident, and is able to summon giant tarantulas. The large Naga Sotuva is a dinosaur, twisted by Chaos to become a nightmarish creature.
Respect Emperor Ashtar, the emperor of darkness! (please log in to view the image)
Maybe we'll meet again... Wandering Flame (one of the best pieces in the Final Fantasy X soundtrack)