Devil is after all an animal, he is staying in the hell in the vision of snake. Some devils are bulldogs, some – other dogs etc. And Satan is fallen angel. He was punished for seducing Eva and was sent to hell for his deed. There are many devils and many satans. God changes them regularly. Some satans (not devils) can be forgiven and taken to the world management. If during their way they develop a lot and start violating justice, God sends them for obliviousness and they forget their way. After some time they wake up and recommence again. Some satans are in the sleeping posture when in hell. God does it deliberately. To become satan is easy, mostly God makes satan out of a person for intention to have His place.