Ysenna

Ysenna is one of the Elder Gods who created the Aether and the original planes. She is often known as "the Physicist", as her role in creation dealt mainly with the setup and manipulation of physical reality.

Later, Ysenna became the sole creator of the material plane of Ysenna, which was named in her honor. This, along with the planes of Aaphobim and [one more here] would later be considered the only major material planes, though many lesser ones existed.