>Why did God create evil?

Short answer: He didn't.

>Who is the father of demons?

Short answer: Satan.

Long answer to both:

God and Satan are 2 eternal, omniscient, omnipotent beings which are independent and polar opposites. God is the benevolent, Satan is the malevolent, and they are both omni- of those qualities as well. They are the sources of good and evil respectively.