Tirek (voiced by Mark Acheson) is an evil centaur and the main antagonist of Twilight's Kingdom. Tirek and his brother Scorpan had a plan a long time ago to rule Equestria together, but soon Scorpan came to befriend the ponies, and tried to get Tirek to abandon their plan. Tirek was imprisoned in Tartarus and Scorpan went back to his home. But many years, Tirek escaped and began stealing magic from ponies. Princess Celestia sent Discord after Tirek, but Tirek offered Discord something better than friendship. Together, Discord and Tirek stole magic from unicorns, pegasi, and earth ponies. Soon, Tirek became so powerful that he even stole Discord's magic, having no use for him anymore. All that was left was the Alicorn magic, which he attempted to take from the Princesses, but they gave their magic to Twilight Sparkle, believing Tirek wouldn't know of a fourth princess. But Tirek did find out, and fought Twilight for the magic, only to reach an impasse. Tirek made a deal with Twilight. The safety of her friends (including Discord) for all the Alicorn magic. Twilight agreed to it. After getting the final key for the box at the Tree of Harmony, the ponies unlocked it and gained the power to stop Tirek and imprison him back in Tartarus.
In the original Generation (voiced by Victor Caroli), Tirek wanted to bring eternal darkness with the rainbow of darkness, and unleash its magic and rule the darkness forever. He met his end from The Rainbow of Light, cleansing the Rainbow of Darkness, and banishing him forever.
Tirek will appear in Twilight's Adventures as one of the main and ultimate antagonists as well as one of the Rainbooms' most hateful and powerful enemies. His first appearance is Twilight and Kyle's Adventures of Equestria Girls: Rainbow Rocks where he is seen being free from Tartarus and helps The Dazzlings and league of Heylin Empire to get The Rainbooms' magic, then rule Equestria and then the world. He later was freed once again from Tartarus by Anubis, and joins the Heylin Empire to destroy The Rainbooms once and for all.