Well, not always was there Rob. First there were the Old Gods. They foolishly decided to have children, who soon outnumbered and overpowered the Old Gods.
So the Old Gods got together in space and decided to create a being of immense power that they could use to control their unruly Godlings.
It turns out that when you combine the best and most powerful of all things from across the universes, you get an unstoppable, and quite raging, Snail.
This snail named himself Rob and defeated the Young Gods and was too willful to be controlled by the Old Gods.
As such, the gods behave to avoid the wrath of Rob.
ALL HAIL ROB! And the land he occasionally calls home....Zimrobwe!