The Skull Knight is a boss version of the Skull Swordsman. He first appeared as the boss of the first stage in Castlevania III: Dracula's Curse, and later returned in a much more powerful portrayal in Harmony of Dissonance. He appears to be the remains of a huge, ancient warrior who has a dragon-like skull, comes armed with sword and shield, and is clad in armor.
The Skull Knight is the boss of the first stage in Dracula's Curse, the town of Warakiya. He can be found in a graveyard at the end of the level, where at first he appears only as a pile of old bones. However, when Trevor approaches, he suddenly comes back to life and reassembles himself to confront the hero. His only attack is a quick downward slash, but he can also damage Trevor by touching him, and this is what he'll try to do, by walking steadily toward him, only stopping every once in a while slash with his sword. He has a considerable amount of HP, but a few flasks of Holy Water should be enough to defeat him in just a matter of seconds.
A stronger version, the Skull Knight King, is the boss of the Caves in the same game. The only notorious difference being that now he will also chuck a series of large bones at the hero.
The Skull Knight reappears in Harmony of Dissonance as the boss of the Skeleton Cave in Castle B. Here he has three forms that change when he loses HP. His first form has a sword and shield, and attacks by stabbing at Juste. After losing enough HP, he falls to pieces. He regenerates from his shield and drops his sword. Now he attacks mainly by dashing quickly across the room. After losing more HP, he repeats his rebuilding sequence, then drops his shield. In this final form he can shoot a large laser from his chest that travels the entire room.
The Skull Knight is one of two bosses in the game which receive non-neutral damage from an element, the Skull Knight being weak to Thunder, and the Golem who, on the contrary, resists to this same element.
It should be noted that in this incarnation, instead of being the remains of a dragon-like creature, he is now the skeleton of a huge warrior who wears a helmet fashioned from what appears to be a bull's skull.