The history of Sith practices in this regard is well-documented, but the most surprising member of this club is the exception that proved the rule: Darth Maul.
At first glance, he seems to have been one of the most obvious and exemplary Siths on record, but the truth is, he was a Jedi first, and he remained one throughout his life, up to the very time of his death. His handler in this double life was Qui-Gon Jinn, who had a vision of the future concerning the matter of the prophecy of bringing balance back to the Force. Jinn realized that the only way he could convince the Jedi Council to accept the chosen one was to die. The only way to ensure this outcome was to find himself an accomplice in making sure it happened that way.
Many years earlier he had identified Maul as a potential Jedi recruit, but Maul had been rejected for various reasons. In secret, he trained the youth anyway and so Maul learned the ways of the Jedi. Maul felt indebted to Jinn and would have done anything for him, but when he learned his hidden master's plan, he was appalled and at first thoroughly rejected it. He changed his mind when Jinn revealed his greatest secret: Maul was Jinn's own child.
It was this very reason that was the basis for the Council's initial rejection, because it proved that Jinn had violated one of the most sacred of the Jedi tenets. When Maul's mother was murdered before his eyes, Jinn realized he had no other choice but to risk his secret being exposed, and besides, he loved the boy.
Together, they suppressed Maul's own memories and thus prepared him for recruitment by the Sith. As a potential practitioner of the Force, Maul was already enticing bait given his penchant for leading with emotion, something he and his father had worked on for years. He channeled all of his worst impulses into an aggressive tendency, although they both knew he controlled those impulses perfectly. Once Darth Sidious approached him, Maul set about the process of faking the development process, appearing to not only learn but be a natural at everything he attempted, his astonishment presented with relish.
It was easy in a way, because Maul's every thought was guided by the certain knowledge of the role he would eventually play as his father's executioner. The thought never less than sickened him. He was disgusted with himself, but his love and respect for Jinn overrode everything else.
He became a man of few words, which was his most calculated move. Father and son had never had the same temperament. Jinn's stolid behavior had provoked an impish persona in Maul, which was how they ended up creating his signature look, the tribal tattoos that accompanied the horns he'd inherited from his mother. He considered himself a devil anyway, no matter how often he reminded himself of the ultimate good they would achieve.
As the years wore on, they saw each other less and less, until the day they were reunited on Tatooine served as a genuine shock to them both. Jinn was amazed at the new fluidity in his son's maneuvers. By the time they clashed on Naboo, Jinn found himself distracted, and so finally learned a part of the role he had asked Maul to play.
He'd known all along that he would die soon after he'd done his part. He kept asking himself, was this selfish of him, to accept it knowing that he wouldn't have to live with himself after he'd accomplished their plan?
The surprise on his face, when it happened, was the result of Maul's decision that if he could have done it all over again, he would. In all those years, he had finally come to understand his father's peace.
He died a Jedi, and a hero.