Hecate

Hecate is the Olympian demigoddess of witchcraft and the night. She longs to rule the Underworld and steal Hades' power over the dead. Hecate only appeared in the Hercules: The Animated Series episode "Hercules and the Underworld Takeover" as the main antagonist.

Personality
Hecate is a dark, embittered Goddess who has always wanted to prove her skills to everyone. Since she comes second best to Zeus, she has developed a sinister, bitter jealousy.

Hecate has no qualms about cheating or deceiving others to get what she wants.

Her personality is so dark and villainous that she exceeds Hades' as she has tried to dethrone and destroy him. Hades even personally admitted he cannot stand Hecate due to her schemes to outmaneuver him.

Physical appearance
Hecate has blue hair and wears a blue headdress. She wears a blue dress, cape, and armbands on both wrists.

Powers and Abilities
As one of the Olympian gods, Hecate possesses all the powers standard to them, such as omnipresence, vast strength, and shape shifting.

As the Demigoddess of Witchcraft, she has vast knowledge of spells and rituals. Because Hecate was the Goddess of Magic, she is the greatest sorcerer of all the Olympians, second only to Zeus. Her Godly expertise in sorcery has spanned even before humanities existence.

She is also capable of pulling off any magical feat that has been displayed by other Olympians that expertise in other areas.

"Hercules and the Underworld Takeover"
After continuous failed attempts to prove she would be a far better Goddess of the Underworld than Hades, Hecate decides to steal his Godhood by taking his flame through trapping a sample in a magic crystal.

While he is busy with the Council of the Gods, she succeeds in taking over the Underworld and taking control of Hades' allies, declaring her intention to collect all the souls on Earth. Fortunately, Pain and Panic escape and seek help from Hercules in overthrowing her.

When confronted by Hercules, Hecate transforms her crystal into humanoid shape. At that moment, Hades returns, with his powers almost depleted and his personality having become mellow. As Hecate started to gloat about her new Underworld order, Hercules destroys the crystal monster, restoring Hades' power.

As Hercules quickly excused himself, Hades exacts fiery punishment on Hecate for trying to usurp his throne.

Hercules and the Disappearing Heroes
Hecate returns to take over the Underworld again, but this time, she kidnaps all the famous heroes from Greece and steals their great abilities in order to create a powerful monster to dethrone Hades. In the end, she is defeated yet again.

Trivia

 * Due to her attempts to dethrone Hades, Hecate is often considered by fans to be the true main antagonist of the Hercules series.