The gemara2 tells us that R' Meir was a descendant of Niron Keisar, Nero Caesar. The Rema Mipano writes that Niron Keisar was a gilgul of Somlah Mimasreikah3 who was from the early kings of Edom. After Niron Keisar converted, his soul began to come for a tikkun, rectification and in the end he was reincarnated as R' Meir who was his descendent and with that he was rectified.
2 Gittin 56a.
3 Breishis 36:36.