The Hebdomad is ruled over by Zaphkiel from the illuminated plane of Chronias, the only remaining member of the seven original martyrs whose souls created the Hebdomad eons ago.
If anyone can even be said to rule in Chronias, that being would be Zaphkiel. Zaphkiel is the mysterious ruler of the Hebdomad, and is the only one who has held his position since it was created; all other previous members having perished in combating fiends or gone on to join the essence of their planes. Zaphkiel embodies the "perfect good," and only the most righteous and exalted individuals can stand in his presence without being consumed. Zaphkiel is the patron of dead children and stillborn babies and watches over their spirits. Beyond this Zaphkiel's motivations and plans are unknowable, though it is known that he intends to make the planes as good as they can be, and only he can promote an archon into the Hebdomad.