When this site was first made Star Wars consisted of two canonical bodies.* The films and the Expanded Universe (EU). Star Wars has developed a fantastic EU over the years. In these stories Han and Leia got married and had three children. The twins: Jaina and Jacen, and a younger son Anakin Solo.
Back when I was in middle school I had the goal of making a Star Wars Fan Film based off of Kevin J. Anderson's "Heirs of the Force". So when it came time to register a domain name "Jacen Solo" was one of the first ideas that came to mind. He was one of the main characters from the Young Jedi Knight book series.
With the creation of the Legends category Jacen Solo is no longer a canon Star Wars character. The case could be made that Kylo Ren is very much a reincarnation of the Jacen character. He is the son of Han and Leia who ultimately fell to the dark side. (In the EU Jacen eventually became Darth Caedus). However, the story arc that Episodes VII and VIII have followed
*Sadly, a few years ago Lucasfilm relegated virtually all EU material to a place it called "Legends". This was done to make room for the stories they wanted to tell in their movie franchises. By the time the newest three movies were in the works pretty much every event had been written about the original character's lives. So to make way for new stories they reduced all previous works except for the Original Six and Clone Wars series to "Legends".