King Sombra is the corrupted, evil unicorn king who enslaved the Crystal empire. He was banashed to the frozen north by Celestia and Luna 1000 years ago, which caused the Crystal empire to disappear alongside it. In the season 3 premiere, the crystal empire and Sombra both return. The elements of harmony manage to stop him once again however, with the help of Spike and Cadence and bring love and peace back to the empire.

Sombra is either shown in his shadow form, or pony form. As a pony, he wears a silver chestplate, shoes and crown, with a red cape.