DDG provides some guidelines which are mythos specific but are otherwise illuminating about the role of worshiper and deity. Greek mythology figures prominently in the sections in the PHB and DMG descriptions of the Outer Planes.
According to DDG, the Greek gods – the Olympians – need the worship of mortals, and a by-product of that need, they take on the qualities of mortals, including petty qualities. The Titans existed before man, therefore they did not require the worship of man – yet so did the Olympians. The need for worship therefore came about after the existence of mortal worshipers.
From this, I take away the following for use in The First Age:
- The relative power of an individual god is based on the number and strength of worshipers
- The more gods need the worship of mortals, the more qualities of the mortals they acquire
- Since only human PCs have unlimited level advancement as Clerics, and supply the most powerful agents, then humans will be of special interest to the gods