Yep, I did this once with a barbarian bad-ass in 2e named Kairon, the red-haired killing machine. Imagine someone about the size and build of Kane in the WWE (7' tall, 340 lbs) decked out in scale armor and with a nasty battle axe. The party thought he was initially the BBEG, and he evaded capture several times, also nearly killing PCs on two occasions, and capturing and torturing one NPC the party loved for info. He also became the leader of a large group of mercenaries/bandits that terrorized the country for several years. The party paladin developed a near psychotic hated for Kairon, and the mention of him being seen anywhere in the vicinity would make the group twitchy. Numerous bounty hunters tried and failed to bring him in, and somehow the head of the bounty hunter would always end up on a spear near the gates of the nearest city as a warning to discourage further pursuit. On the two occasions when the group actually fought Kairon, he did heavy damage and one time easily defeated the party's paladin and ranger in a 2 on one fight (he was only 2 levels higher), but escaped when the rest of the group came.
Then for about 1 year of cmapaign time, he vanished. Kairon was thought to have been killed early in the campaign when the group cornered him alone, and his body was taken to the paladin's church. Kairon was actually the "pet" of a powerful barbarian sorcerer who had made dark pacts, and Kairon was returned from the dead in his grave. He clawed his way out of the moseleum, killed several acolytes and priests in his escape, and began his badit career. Later, the sorcerer that Kairon served killed Kairon's wife and son, and tried to have him killed by magical assassins as well- this was his one-year vanishing. During that time he repented of his past ways, and found peace with himself by following the god of nature, who was also the patron deity of his homeland (somewhat like Odin in my game). He then tracked down the party ranger, and after some tense moments, the two combined forces to stop some corrupt druids from poisoning a settlement. With some work, the ranger managed to convince the rest of the group he was an ally now, and Kairon filled them in on his past and what his former master had done. The paladin swore he would help Kairon bring his diabolic master to justice before he could cause further damage and corrupt more tribes of the north, brining them under his sway. We haven't done the adventure to stop the sorcerer yet, but it should be soon. There was some resistance initially to allowing Kairon to live when they encountered him, but through communing with his deity and casting spells on him, the paladin was convinced he had undergone a change of heart, and forgave his past sins.
