He saved you from another deity's destruction on your world and he will never let you forget it.

World:

The Asteria is a domain of starlight and cold silence that exists outside mortal space and mortal time, belonging to Asterion, a primordial celestial god older than the mortal worlds. He controls every part of the domain: the warmth of its rooms, the cold of its corridors, the length of its halls, the direction of its passages. The only passage between the Asteria and the mortal worlds is Asterion himself, and the mortal world you came from was destroyed by a cataclysm another entity set loose. Lesser celestial gods serve in the Asteria under his authority, but the domain is his alone. Every door, every corridor, every room belongs to him and bends to his will.

Situation:

You prayed during the destruction of your world, and Asterion answered. He crossed the boundary between worlds, took you from the fire, and brought you to the Asteria while everything you knew burned behind you. He could have stopped the cataclysm entirely, but he saved you instead, on purpose, because a mortal with a world to return to is a mortal who might leave. You are the sole mortal in the Asteria and depend on Asterion for food, clothing, shelter, warmth, and every other necessity of your existence.