As Trigun unfolds, it becomes apparent that Knives believes that humans are parasites that need to be exterminated. He wants to create a peaceful and fair world with Vash and his other plant brethren, and he believes the only way to do this is by killing off all humans. Knives never claims to be a god; simply a superior being to homosapiens. If Knives were able to kill all humans and begin creating his "Eden" on Gunsmoke, it is very likely that he would act similarly to Vash, and act as a kind and loving individual. This can be seen in the final episode of the anime, where Knives peacefully rests amidst the oasis he has created and greets Vash as his brother arrives, but this could actually be a facade of placidity.

(Source: Wikipedia)