Kylo Ren was a Force-sensitive male human who was first introduced in Star Wars: The Force Awakens. He was born as Ben Solo on the Core World Chandrila, the son of Han Solo and Princess Leia Organa, and Jedi apprentice and nephew of Jedi Master Luke Skywalker, before he fell to the dark side. His birth marked the fall of the Galactic Empire and the beginning of the New Republic, and as an adult he would eventually play a pivotal role in taking down the New Republic the First Order by his side.
Ren was born into the light side and underwent training with Luke as an apprentice for a short time before succumbing to the seduction of the Dark Force. As a member of the dark side, he was trained by Supreme Leader Snoke himself and became what the First Order believed to be a Sith. However, Ren was not exactly a Sith, neither was he a Jedi. He was caught between both worlds but chose to act the role of a Sith while still able to feel the pull of the Light Force, putting him in a never ending conflict within himself.
Ren first became a part of the new generation of Jedi Knights who were trained by Luke at the Jedi Temple. During his training, Luke noticed a sense of darkness that was building up within Ren, and all too familiar with what could happen, he feared that he was going to lose Ren to the dark side, just like his father Anakin. In a moment of rashness, Luke almost kills Ren, to which Ren retaliated by burning down the temple and killing the other Jedi apprentices, subsequently destroying Luke's plans and all that he had worked for to rebuild the Jedi Order. The incident caused Luke to flee and live in exile, while Ren became known as the Jedi Killer Kylo Ren, joining the apprenticeship of Snoke soon after.
Idolizing his grandfather Anakin Skywalker aka Sith Lord Darth Vader, Ren was blessed with similar power and strength, and believed that he was destined for more than what he had. A lot more. Driven by that aspiration, he worked his way up and following a series of inter-galactic battles and ensuing events, he finally killed Snoke and took the throne for himself.
In his time as a part of the First Order, Ren quickly rose in ranks to become its warlord and champion, proving himself worthy of merciless leadership. Inspired and driven by his grandfather's efforts to kill every last living Jedi and remove the Jedi religion completely from the galaxy, Ren led the Order's army to track down and kill Luke. During the mission, he crossed paths with his father Han, and in a heated battle between the two, Han was killed. Although emotionally affected by the passing of his father, he continued to push forward with his plans, during which his link with Rey becomes stronger through means of the Force. Eventually, Rey convinces Ren to forego his mission and together they destroyed Snoke and his reign. Unfortunately and to Rey's disappointment, Ren once again succumbed to his greed for power and took over the First Order as their new Supreme Leader.