For the ancient Hebrews, the most powerful living men virtually ranked among the gods. Thanks to Plato, today we think of God as infinite, something beyond human scope. But ancient people hadn’t been taught about infinity, and they viewed their gods as finite. Their gods were immortal, but they were not all powerful or all knowing. A mortal could never be divine, but a mighty ruler could be godlike. The ancient Hebrew Psalms praise King David as the son of God, in language that would later be applied to Jesus. Ancient Hebrew judges were sometimes known as “elohim,” the mighty ones. “Elohim” also means “the gods” or “God.” Hadad the Edomite, on the other hand, was a “satan,” or adversary. Yahweh called him up to challenge King Solomon. Today, “Satan” is a spirit, but that tradition is later, starting in the Book of Job. For the earlier authors of the Bible, satans were mortal enemies of Israel. They were flesh and blood. And it wasn’t just the Hebrews who saw the mightiest mortals as nearly gods. Asia, Africa, Europe, and the Americas all had their god-emperors. Mighty mortals ruled the world, if not as gods then nearly so.
A modern reading of history might agree. The world was and is ruled by mortals. The mighty judges of the earth—people like Alexander, Caesar, Jesus, Confucius, Muhammad, Jefferson, Lincoln, Stalin, and Hitler—were flesh and blood. They were born, they changed the world, they bled, and they died.
For that matter, original D&D had precious little to say about the gods. The powerful beings that ruled the campaign map were mortals: lords, wizards, and patriarchs (or evil high priests). Top-level PCs could build strongholds, and the mightiest creatures in the land were top-level NPCs in strongholds of their own. The setting was dominated by powerful, archetypal mortals. The gods were implied but not named. Even clerics needed no connection to any particular deity or pantheon.
13th Age has consciously followed suit, basing the game world on mortals rather than on deities. (The Lich King isn’t strictly mortal, but he’s within striking distance.) The interactions of the mortal icons help create dynamic tension in the campaign. Their precarious balance is a ready source of conflict and change. Mortals work as campaign elements better than gods do. The icons can have normal human motives and weaknesses. Most of them are fated to die, just as many icons have done before them. As mortals, they are closer to the player characters than gods would be. They’re more present and more real. Maybe some day you could even have lunch with one.
The gods in 13th Age, on the other hand, are indeterminate and free-form, as they were in original D&D. If there are particular gods you want your character to worship, there’s room for those gods in the campaign. If the GM needs to invent this or that god for some nefarious purpose, there’s room in the setting for it. The gods don’t define the campaign; the campaign defines the gods.