Quite simply: Anything you can think of. If you believe a god exists, it does. The more people that worship said god, the more powerful that god is. All the ‘gods’ are simply a person holding the Mantle of that god. If they die, the Mantle passes to the person who is closest that is capable of doing the job. The Mantle may choose to overlook an individual for it’s own reasons; there is no exact science to a Mantle passing on and you cannot accurately predict where it will go.
One note: Some gods may be so similar to another that they are simply absorbed into it’s domain of influence, combining the two into one person who holds both Mantles.