A non-playable race in the Blizzard game Starcraft. Heard of only in the storyline, though never portrayed, they are supposedly the creators of the Protoss and the Zerg. The Xel'Naga creatures roamed the universe in travelling "worldships", and breathed life into several species, in an attempt to create the perfect lifeform.
The Protoss presented the purity of Form.
The Zerg presented the purity of Essence.
Though the Xel'Naga are now extinct, if the Protoss and Zerg would ever merge into one species, they would represent the Purity of Being.
Whispers of the Last of the Xel'Naga remain.