In canon Edit
Jacen began as a bright-eyed kid, a trainee at Luke Skywalker's new Jedi academy. He went on various wacky adventures with his siblings and other young Jedi trainees, dating back to when he was but two years old and the disembodied spirit of his Uncle Luke possessed him (long story).
As he grew, he became a respected Jedi Knight, but showed a distinct predisposition toward brooding and general nuttiness. A creepy Fosh named Vergere, who worked for the Yuuzhan Vong, took Jacen under her wing and taught him of the Potentium, the belief that the Force has but one, entirely neutral side. With this knowledge, Jacen defeated the Big Bad behind the invasion.
Jacen finally went entirely bonkers when the current Dark Lord of the Sith, Lumiya, screwed with his head and gave him the idea that his uncle Luke was trying to establish a new Galactic Empire. Caedus went on to do exactly that, in the process bumping off several recurring characters and unleashing a plague, finally answering for his crimes with his sister Jaina's lightsaber through his gut.
PPC Assessment Edit
Jacen, especially as Caedus, hits several badfic bullseyes. He is handsome, angsty, evil but not irredeemable, and his final storyline is incredibly divisive among the fandom and may result in discontinuity and Fix Fic. It would be advisable to keep him watched.