YHWAH.

"Before He gave any shape to the world, before He produced any form, He was alone, without form and without resemblance to anything else. Who then can comprehend how He was before the Creation? Hence it is forbidden to lend Him any form or similitude, or even to call Him by His sacred name, or to indicate Him by a single letter or a single point… But after He created the form of the Heavenly Man, He used him as a chariot wherein to descend, and He wishes to be called after His form, which is the sacred name YHWH."

(Zohar, part ii., section "Bo", 42b)