Jacen Solo was the main protagonist of the New Jedi Order series. He is the son of Han Solo and Leia Organa, the brother to Jaina and Anakin Solo. He is also the nephew of Luke Skywalker and Mara Jade Skywalker, the cousin to Ben Skywalker, and grandson of Anakin Skywalker and Padmé Amidala.
A Jedi Knight, Jacen was well known as the hero who saved the galaxy from the Yuuzhan Vong. He continued to be seen as a hero until his fall to the dark side in the Legacy of the Force series, in which he became the villain Darth Caedus. He serves as the main overarching protagonist of the New Jedi Order series, the main antagonist of the Legacy of the Force series, a posthumanous character in Fate of the Jedi, and a major supporting protagonist in several other Legends stories.
Though part of Legends are not canon for the films, Jacen Solo's character inspired Kylo Ren for The Force Awakens and onward.