how did Genghis Khan become a ruler?

Question

and also what made him want to be a ruler

Answer 1

How is the subject of many documentaries and too vast to describe here. You could say it was because he was ruthless, demanded discipline and new no bounds to his quest.

I think he was driven by revenge and the fact he had lost all that was meaningful to him meant he had nothing to recover as an indicator his mission was accomplished. His goal was to continue expanding his power and rule.