An indescribable monster and its army (the Slayers) attack the planet Krull. In order to stop the invaders, two hostile nations decide to join their forces by the marriage of Princess Lyssa and Prince Colwyn. During the ceremony, the Slayers attack the palace, kill both kings, wound Colwyn and kidnap Lyssa. The next morning, the wise Ynyr seeks and finds Colwyn. With Ynyr's help, Colwn gains possession of a magic weapon, a five bladed sword, and together they go on their quest for the indescribable monster's black fortress to free Lyssa.

Frank Price, then-president of Columbia Pictures, determined that an unknown American actress would help state side ticket sales as opposed to an unknown English actress. With that logic in mind, Price met with Lysette Anthony and informed her that all of her dialogue had been dubbed by actress Lindsay Crouse. Anthony was totally unaware that her voice was to be dubbed prior to the meeting.

Prince Colwyn:
The forest is not safe. You best travel with us.


Ergo:
Me travel with you? Do you know who I am?


Prince Colwyn:
No.


Ergo:
I am Ergo the magnificent. Short in stature, tall in power, narrow of purpose and wide of vision. And I do not travel with peasants and beggars. Goodbye!

Revealing mistakes: When Rell is being crushed between the walls of the fortress, the walls are obviously made of soft elastic material.