Pain Rikudou

Pain is not a single person, but the result of a ninjutsu from a shinobi from Amegakure named Nagato. Pain's name comes from Nagato's ninjutsu "the six paths of Pain", which he developed after the death of one of his best friends. The technique allows him to control and manipulate up to six corpses at will, just like his own body. So, strictly speaking, Pain is not just one person, but six corpses controlled by Nagato. So you could say that Nagato himself is Pain, since he created the technique.