Was Satan formerly an angel? I have heard people mention this in passing numerous times, but I can't find a scripture that directly supports this. If he wasn't an angel, where did he come from? — John Knuckey (San Francisco)

You are right, there is no scripture which directly says Satan was an angel. The commonly cited Isaiah 14:12 may shed light on the matter, but in context it is referring to the king of Babylon, as the chapter explicitly states. (The same could be said of Ezekiel 28, which refers to the King of Tyre.)

So where did he come from? God created him, since God is the Creator of all. And since everything God created was good -- at least to begin with! -- Satan must have used to be good. But he changed; he rebelled. And apparently other spiritual powers followed him. The traditional, Roman Catholic understanding must be pretty close to the truth. And -- yes! -- he masquerades as an angel of light (2 Corinthians 11:14). "Masquerade" doesn't necessarily mean he isn't an angel, only that he isn't an angel of light. For he is the angel of darkness.

HOWEVER, there is an alternate view worth considering. The link below provides a brief excerpt from one of Pepperdine professor Ron Highfield's books, The New Adam: What the Early Church Can Teach Evangelicals [and Liberals] about the Atonement (Eugene, OR: Cascade, 2021), 53-54.