Who defended the devil's salvation?

As the question states: who defended the devil's salvation? I know I've read of a Catholic saint who supposedly defended the devil's salvation. And why not? Maybe the devil has been greatly misunderstood in the great plan of God? Anyways, I've searched, and the closest I could find was Lawrence Justinian, a Catholic priest and a saint within the Catholic Church. I also know that I've read that this person, maybe a philosopher, was a contemporary of St. Thomas of Aquinas. Does anyone know any of this?