Zekrom (death), Reshiram (life), and Kyuurem (nothingness) are created when Arceus notes that Pokemon populations are very volatile; should Mortals kill eachother, Reshiram would create new life; should Mortals become too populous, Zekrom would annhilate alll of them; should Arceus become bored with creation, Kyuurem would cause the Big Crunch and restart the universe