Who was the commander of the naval forces in the pacific during World War 2?

The combined Allied Joint Chiefs split the Pacific Theater into two major operational areas: the Southwest Pacific Area, and the Pacific Ocean Area, each of which had a Supreme commander, which reported to the Combined Joint Chiefs.

General Douglas MacArthur was the supreme commander for the SWPA. Most major land invasions and defenses fell under his command, however.

Admiral Chester W Nimitz was supreme commander for the POA. All major naval operations in both theaters fell under his command, however.

Frankly, this was a political compromise, and was sub-optimal as the two commands ofen competed for resources and priorities.
Adm. Patrick M. Walsh