@pry @raz @am @lilli your friend is wrong. monist belief in many Gods representing one supreme God dates to the Rig Veda and identification of the brahman with a strictly singular atman/paramatma dates to the upanishads at least. The two largest streams in Hinduism since the Bhakti movement have been Vaishnavism and Shaivism, both which have supreme gods (vishnu and shiva respectively). There is not a single hindu tradition I can think of which isn't monist regarding the brahman.