According to show’s writer’s Bible he’s a wizard; his magic is most clearly manifest in his Rainbow of Darkness. The Rainbow of Darkness is a powerful force of black magic seemingly equal to the ponies' Rainbow of Light. The Rainbow of Darkness can also distort reality and transform living things into his bestial slaves, among other things.
In “Escape from Midnight Castle,” he has made the decision to use his Rainbow of Darkness to bring about never ending night and to that end dispatches Scorpan to kidnap four ponies. His plan is to turn them into freaks with his magic so that the deformed and now monstrous ponies will pull his chariot through the air and thus enable to bring about “The Night that Never Ends.” When Scorpan fails to bring enough ponies after a raid on Dream Castle, Tirek threatens to behead Scorpan’s foster son Spike. The centaur sees a chance, however, when a pony rescue party led by human heroine Megan Williams inadvertently brings the last ponies he needs to complete his scheme.
After transforming the last pony, Tirek flies into the air atop his demon-pony pulled chariot in order to complete his scheme. He also grievously injures Scorpan who had reformed by that point and takes back the pouch which contains his Rainbow. After a brief battle with his forces, Megan tries to use her Rainbow of Light against Tirek’s Rainbow of Darkness but it is quickly enveloped by Tirek’s magic. To the centaur’s shock however the Rainbow of Light overpowers his Rainbow, and brutally kills him; he dies screaming and is vaporized. Upon his death, those who had been under his power revert to their true form and Midnight Castle ceases to exist.
Tirek is shown to be a sadist who delights in humiliating his followers and to be capable, not only of murder, but of infanticide. He is thus far the only villain explicitly shown in canon as willing to kill and the only villain who in turn deliberately was killed by the series's heroes. He is seen by various fans as the pony equivalent of Satan  and on a Cracked.com list of villains out of all proportion to the innocuous heroes they faced, he was ranked number one.
He is voiced by Victor Caroli, best known as the narrator of The Transformers.
Friendship is MagicEdit
After many years of absence, Tirek would eventually be revamped for My Little Pony: Friendship is Magic, the current generation, and appeared as the main antagonist in the season 4 finale of two parts "Twilight's Kingdom".
- 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 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.