Maha Brahma is a realm, and not “A GOD”. Any living being (including each of us) has been in all realms in this beginningless sansara. We have been at the highest (except the five pure abodes in rupa loka which can be accessed only by Anagamis or Non-Returners). One time the Buddha pointed to a bunch of ants on the ground and told bhikkhus that each of those ants had lived in a brahma loka. The sansara is that long; there is no discernible beginning. These 31 Planes of Existence is described in the Dhammacakkappavattana Sutta. It lays out the “blueprint” of Buddha Dhamma.
In the realm of Great Brahmas (Maha brahma) Buddha mentions about one Great Brahma, a deity whose delusion leads him to regard himself as the all-powerful, all-seeing creator of the universe. It is in Kevatta (Kevaddha) Sutta: To Kevatta (DN 11). Kevaddha Sutta informs one of what even a “God” does not know. Maha Brahmas, like Baka, think they’ve gone beyond anything the Buddha knows, so the Buddha has to go up to their Brahma heavens and subdue their pride, to show them that they still have more to let go of, that there is something the Buddha himself has gone beyond but they haven’t.
To be continued….