The Holy Mother Church claims that Satan was originally God's favorite angel. God, who is perfect, and certainly capable of perfection, designed and built a defective Head Honcho Angel, Lucifer (the Light Bearer) and some less charismatic follower angels, Beelzebub, Azuriel, etc. who joined him in a rebellion against God. Why he did this is pretty hard to understand. Was he defective, or did he become defective? Do angels going bad on us present a problem, and how would we address this? The Bible does not say.
I have yet to see my first angel. When I hear a bell ring, I look around to see if anyone has sprouted wings, but as of yet, I have seen nothing of this. I have not even seen anyone who could pass for John Travolta, let alone an angel.
God (being more powerful) defeated the defective angels, but did not destroy them and they went to Hell, which may or may not have been designed by God or Lucifer.
That was all so presumably people could have a choice between Good and Evil.
There are no figures as to the numbers of angels or demons that exist, the Holy Mother Church claims that God is the most powerful.