Khyar, a.k.a. the "Mad Prophet", was a protoss seer.
At some point Khyar wrote several cryptic passages concerning a mystic Acropolis referred to "The Six and The One", namely that "...the ruler of the Six shall use the One to become the Only...".
1998-10-09. Acropolis. StarCraft Compendium Map Archives. Accessed on 2007-11-03.