The Helmasaur King is a boss in The Legend of Zelda: A Link to the Past. Serving as the main threat in the Palace of the Darkness. His Japanese name is ジークロック(Jīkurokku).
He was a decent boss though I wish he was a bit smaller. I don't like bosses that take up half the screen.
He also returned in Four Swords on GBA as a remade boss. Meaner and greener.