Merlin the Wizard is the only person in Dark Castle which is not an enemy. He gives Prince Duncan the Fireball as a reward for making his way to him. After the events Dark Castle Merlin helps Prince Duncan find his way to the Ante Room, located behind the Black Knight's throne, and further informs him of the mysterious Orbs which are needed to open the gate to the Final battle with the Black Knight.
Merlin is also said to be the maker of all the Elixirs scattered through out the Castle.
- In Dark Castle Merlin is in a Cave, and reads in his book. When Prince Duncan comes to him, he gives him the Fireball.
- In Beyond Dark Castle Merlin is in the East Tower Top. When Duncan goes to him with the Orb, he grants him the power of the Fireball.
- In Return to Dark Castle Merlin is in the levels from the previous two games, but also in more levels.
Merlin has stayed looking the pretty much same since the original Dark Castle, with the only real changes being color.
- In Dark Castle if you long jump into him, zaps you to death.