Twili
The Twili is a race of beings who inhabit the Twilight Realm. Most of the inhabitants are of the "monster" variety throughout your adventure, due to Zant's evil rule. However their true forms are more impish in nature with black and red markings while other members of the race have more human like bodies like Zant and Midna.
Enos ago, the Twili were a tribe of Hylians that was sent to the Twilight Realm by the Sages of Hyrule. This was punishment for their misgiven attempt to use old magic to claim the Triforce. Thier "old magic" became known as the Fused Shadows, a powerful instrument, however their powers proved too weak for the power of the gods. They were banished and their Fused Shadows were split into three pieces and scattered throughout the realms. This tribe lived in the Twilight for centuries until they evolved into the Twili, mere shadows of what they once were. While some came to love the beautiful peace that can be found only in Twilight, it drove some of it's inhabitants mad. Midna became the Twilight Princess, but was upsurped by Zant toward the beginning the of The Legend of Zelda: Twilight Princess. It is revealed that Zant was next to become Twilight Ruler, but was passed over. In a terrible rage, he used the power of his false-god, Ganondorf, to transform most of the inhabitants of Twilight into monsters. Zant also transformed Midna into an imp. Midna's only hope was to find the magic of her ancestors, the Fused Shadows.
The events described in Twilight Princess was not specified to occur before or after the events of Ocarina of Time, officially the first Zelda game in the timeline, it is also never made certain, although hotly debated weather or not the Twili had any inclusion the events that lead to the creation of Majora's mask as one would assume that the Mask was also forded before the events of Ocarina of Time