According to the Beyonder's story, this creature existed before the Omniverse and created the Beyonders, imbuing them "with the tiniest fraction of his power".

Source: https://screenrant.com/marvel-the-lost-one-new-secret-multiverse-beyonders/

At least, that is how the situation appeared until Captain America took it upon himself to call out the true mastermind of this entire plot, and his doing so has thrown all the Beyonders' plans out of synch.

Source: https://www.cbr.com/all-out-avengers-cosmic-confrontation-beyonder-marvel/