Note: Details are currently vague about this portion of this particular Mistake. It may be altered and revised as time goes on and more information is revealed.
Details on how his parents met, as well as the details of his conception, are scarce, and it's doubtful that Cain even knows. What is known, however, is that the Emperor had him sent away, and that he was raised by Sylar.
Over time it became apparent that he had inherited a measure of Force-sensitivity from the Emperor, and he began to hone it. It is reported that he has a talent for Force Lightning. As well, Cain inherited his father's vision and desire for a better world- by any means necessary. To this end, at the age of 18, he went to college to study law, business, and political science. As well, he became a Senator's aide to allow himself experience in the field. He realized, however, that even in a genuine position of government, the good he did was extremely localized and was often mitigated by self-serving politicians. In response, Cain took to using their tactics against them, being as underhanded as necessary to achieve good.
Over time, it occurred to him that because humanity was so divided, the only way to achieve peace, and therefore a better world, was to unite them under a single banner, as a single political entity. In his mind, as he had inherited Sylar's "might makes right" philosophy, there was only one person capable of bringing a fractured and divided race together: himself.
To this end, he has maneuvered himself through the American government, slowly climbing the ladder, planning to, one day, take office as President, and unite the rest of the world under him, by any means necessary.
Cain is a calm and nominally gentle person. But, when faced with an obstacle, he is adamant in his resolve to overcome it, and cannot be swayed. He genuinely does want to help the world, but he is willing to sacrifice his morals to do it.
Perhaps as a result of being descended from Sylar, Cain has a hunger for Force energy. Normally, he sustains himself on the ambient Force energy of those around him, much as a force crystal does, but he can drain Force-users in such a way that it can weaken, or even kill them.