(spoiler warning!)
Jacen Solo was the eldest son of Han Solo and Leia Organa Solo, the younger twin of Jaina and the brother of the late Anakin. Even before he and his sister were born, their uncle Luke Skywalker could sense their strong presence in the Force, for the twins shared an inseparable mental bond. Later in his life he became the mentor to his cousin, Ben Skywalker and fathered a baby girl, Allana, with Tenel Ka.
Jacen showed latent Force powers as an infant when he helped his uncle and his uncle's students defeat the spirit of Exar Kun. He started his formal Jedi training years later at his uncle's Jedi Praxeum on Yavin 4. He excelled as one of the best students, getting into many adventures with his friends Lowbacca, Tenel Ka and his sister Jaina. Later, during the Yuuzhan Vong War, he often did not see eye to eye with the orthodox Jedi view of the Force, despite being one of the more powerful Knights of the New Jedi Order.
After being captured by the Yuuzhan Vong, he became associated with Vergere, who molded many of his ways of thinking. Jacen had always been an empathetic person, forming close bonds with Humans and animals alike; as a child he developed an affinity and sensitivity towards nature and the Living Force. However, this bond with living beings diminished severely after his encounter with Vergere. By 40 ABY, Jacen's empathy to others had become largely nonexistent as a result of falling to the dark side, a trait evidenced by his remorseless torture and killing of suspected terrorists. In 40 ABY, he secretly apprenticed himself to Lumiya, becoming her Sith apprentice, and, after her death at the hands of Luke Skywalker, Jacen declared himself Darth Caedus, Dark Lord of the Sith, bringing the Skywalker legacy in full circle
