Lord Tirek

Lord Tirek is the primary antagonist of the two-part fourth season finale episodes. He is a villain who escapes Tartarus and steals magic.

Development and design
Tirek shares his name and certain aspects of his design with a Generation 1 villain. During her takeover of the Hub Network's Twitter feed, Meghan McCarthy described Tirek as having "some serious issues and some serious magic".

Twilight's Kingdom - Part 1
"It's Princess Celestia and Princess Luna that find themselves awakened by visions of Tirek's arrival, recalling that he and his brother SCORPAN had once set their sights on Equestria, aiming to steal all of it's [sic] magic. After Scorpan befriended a young unicorn wizard, he attempted to halt Tirek's plans, but had to inform the ponies, and Tirek was exiled and imprisoned, while Scorpan returned to his homeland.

"Dropping in like MARY POPPINS, Discord is called upon by the ponies to help track down the escaped Tirek, but putting their faith in Discord is a grave mistake, as Tirek - who becomes not only stronger, but larger in size with each pony defeated - is a persuasive influence, who quickly convinces the weak-minded Discord to switch sides."

Twilight's Kingdom - Part 2
"As Tirek continues to hunt down each pony to steal their magic, he eventually grows strong enough to steal the power of flight, and then goes after the Earth ponies as well. Even Discord finds himself betrayed, as Tirek devours his magic and deems him  'just as worthless'  as his brother, Scorpan. Only expecting there to be three Princesses, Tirek desires to make their Alicorn magic his final conquest... but with Twilight Sparkle a wildcard, Celestia, Luna and Cadance give up their magic, bestowing it upon Twilight in hopes that Tirek will not find it.

"Evenly-matched, Tirek and Princess Twilight Sparkle face-off in battle, their powers bringing them to a draw. What hangs in the balance is the freedom of Twilight's friends, all of whom are now being held hostage in exchange for her magic... so she sacrifices her power, but that allows her the final key to opening a mysteriously-locked chest that she'd been trying to open. Held within, the rainbow power consumes Twilight and her inner circle, allowing them to defeat and imprison Tirek once more, while proving once and for all that 'friendship is magic.'"

Quotes
""Is he friend, or is he foe?", the pony wonders? I can assure you... I am no friend. I am Lord Tirek, and I will take what should've been mine long ago."

- Twilight's Kingdom - Part 1

"Everypony will bow to my will."

- Twilight's Kingdom - Part 1