I don't think it's much of a spoiler to reveal this, but Darth Vader is Luke Skywalker's father. If Vader doesn't exist, how did Luke come to be? Now take the answer to that and apply it to your question.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'
