King Sombra

King Sombra, or simply Sombra, is a male initially-umbrumunicorn, the former tyrannical ruler of the Crystal Empire, and the main antagonist of the season three premiere, the season ninepremiere, and the IDW comics' thirteenth story arc. Princess Celestia tells Twilight Sparkle that he took over the Crystal Empire a thousand years ago but was banished into the frozen north. Before his banishment, King Sombra put a curse on the Crystal Empire which made it vanish into thin air. When the Empire returns, so does Sombra, who attempts to retake it. He is defeated by Princess Cadance and the Crystal Ponies' use of the Crystal Heart.

In The Beginning of the End - Part 1, Sombra is restored by Grogar to join him in an alliance with other villains so they can conquer Equestria together and defeat Twilight and her friends once and for all. However, Sombra tries to take over Equestria by himself and, despite being able to destroy the Tree of Harmony and the Elements of Harmony and conquer both Ponyville and Canterlot, he is defeated again by the Mane Six.

In the comics, after his defeat at the Crystal Empire, he returns again with help from Radiant Hope and eventually reforms.

In When the Cold Breeze Blows Away, he would be mentioned in during World War III since his defeat that he can be mentioned in history of Equestria and the Crystal Empire

He also mentioned in Great Crystal War's history but then the Great P365 War happened, he would be mentioned in Onyx Sorbetstorm's picture

Instead of destroying the Tree of Harmony and the Elements of Harmony, New Group P365 would create their undead hordes that Onyx Sorbetstorm is the one who first created the Element of Dead Spirits.