Considering Satan is a fiction, I’d say Satan can be whatever you want him to be. It doesn’t help that the Bible doesn’t actually explain what happened to cast Satan into Hell other than there being a war in Heaven. Pretty much all we get is Revelation 12:7-10.
7 Then war broke out in heaven. Michael and his angels fought against the dragon, and the dragon and his angels fought back. 8 But he was not strong enough, and they lost their place in heaven. 9 The great dragon was hurled down—that ancient serpent called the devil, or Satan, who leads the whole world astray. He was hurled to the earth, and his angels with him.
Also, there’s Isaiah 45:7
I form the light, and create darkness: I make peace, and create evil: I the Lord do all these things.
So if God creates evil, what does Satan even do? Carry out his work for him? That seems to be what Twain thought when he wrote Letters from Earth. Seems as good a source as any.