In Hinduism, is God one or many?

In Hindu Dharma, God is One.

“Ishvara” means That which is omnipotent (sarva-shaktimaan). Two omnipotent beings cannot exist, because it is not logically possible: if there were two omnipotent powers, each would limit the other. Therefore, like the other major religions, Hindu Dharma also accepts that God is One. He is called Brahman — or Para-Brahman.

That one Para-Brahman Parameshwara reveals Himself in many forms at the time of creation.

This raises a sensitive and beautiful question — if God is one, why does He have so many forms? Is He really formless, or with form?