Tirac

Tirek is a demon with elements of a centaur. He resides in the forbidden Midnight Castle alongside his minions and his servant/slave Scorpan, who he orders to kidnap the ponies of Dream Valley to execute his evil scheme.

Tirek wields the Rainbow of Darkness, a powerful sack containing evil magic which corrupts everything it touches. It can even turn the ponies he captured into evil dragons which were used to pull his "Chariot of Darkness" and execute the event called the "Night that Never Ends", on which he will use the Rainbow of Darkness to corrupt Dream Valley and plunge it into chaos. When Tirek takes off in his Chariot of Darkness, Megan grabs the satchel containing the rainbow of darkness, but can't hold on to it. As he was about to release the Rainbow of Darkness, Megan opens the locket to reveal the Rainbow of Light. But it's only a small piece that is soon enveloped in darkness. But the Rainbow of Light starts fighting back, and eventually overpowers the Rainbow of Darkness. Tirek was destroyed by the Rainbow of Light, freeing Scorpan from his spell and turning him back into his human form.

Tirek will appear in My Little Pony Friendship is Magic in the two parter episode Twilight's Kingdom.

Trivia

 * Tirek was the first threat that required the Rainbow of Light and is also the reason the Little Ponies came to the real-world, resulting in the events that would start the Generation 1 Series: he was also one of the more serious and malevolent villains in the show (which is saying something as most early villains were greedy, corrupt and only a few redeemed themselves).
 * Tirek was a Devil figure who sought an eternal night and used the Rainbow of Darkness to transform Little Ponies into horrific monsters, alongside anyone else who opposed him.
 * Tirek was surprisingly violent as well, when Scorpan failed him several times he threatened to behead Spike as punishment (this is exceptionally wicked as Spike is a baby dragon).
 * Tirek shares some similarities to the My Little Pony: Friendship is Magic villain, King Sombra. Both are one of the darkest and most malevolent villains in their respective generation, both are associated with darkness, both have tried to kill Spike, and both are destroyed in the end.
 * The "Night that never ends" aspect is shared with another My Little Pony: Friendship is Magic villain: Nightmare Moon. Accordingly, it's often stated that she had been brainwashed. Many speculated to be by Tirek himself.
 * Tirek is often spelled Tirac.
 * In Tirek's first scene, his face is not seen, and he is running his hand across the Rainbow of Darkness as if petting a cat. This is most likely a reference to the James Bond villian, Ernst Stavro Blofeld.
 * Tirek is the only confirmed Generation 1 villain to return in Generation 4, albeit in a different incarnation.