Question

which ruler broke with the egyption practice of worshipping many gods and declared that egyptians should worship only aten the sun god

Answer 1

I think it is Akhenaten the ruler that  broke with the egyption practice of worshipping many gods and declared that egyptians should worship only aten the sun god. He is especially noted for abandoning traditional Egyptian polytheism and introducing worship centered on the Aten, which is sometimes described as monolatristic, henotheistic, or even quasi-monotheistic.

Answer 2

Akhenaten is the ruler who broke that practice. I think.