A long, long time ago, during the times where Gods roamed about freely in the Universe. The situation was quite relaxed in comparison to what it was now. Each God had their own place to live, a planet, sometimes an entire galaxy.
But then beings started taking birth in the universes that they ruled. Strange beings that were really… weak. They lived faster than the Gods; they reproduced, which Gods couldn't do, then they die as their time passes.
It wasn't a one place phenomenon, but it was more or less taking place in the entire multiverse. This really intrigued all Gods as they wondered what could have happened that triggered this phenomenon.
Some Gods simply wiped all those beings which were in their universe, others amused by them decided to watch over them. Some presented themselves in front of them, making them worship the God.