Hudnos is the main villain and final boss from Knightmare. Said to be the King of the Underworld, Hudnos kidnapped Aphrodite, the goddess of love, and trapped her in the Nightmare Castle. Popolon, a brave knight who loved Aphrodite, sets out to rescue her.
Popolon, unable to find the Nightmare Castle, ends exhausted and falls asleep, having nightmares of monsters threatening Aphrodite. In one of his dreams, the goddess Hera speaks to him, revealing that Hudnos hid the Nightmare Castle beyond Mount Atos, urging him to follow the trail left by Aphrodite and rescue her.
Popolon sets forth to Mount Atos, finally finding the Nightmare Castle where Hudnos was hiding. Popolon defeats Hudnos and rescues Aphrodite, taking her back with him to the Greek Kingdom. Upon returning home, however, Popolon finds the place desolate and the Greek Castle overrun with monsters. It is then he discovers that the whole kidnapping was just a ruse to take him away from Castle Greek, as Hudnos was just one of the demonic minions of Galious, who had taken over the castle.