The solos

Driver claimed that he was privy to several details of Kylo Ren's backstory during the making of the films. According to Lev Grossman, who interviewed the actor in the lead-up to The Rise of Skywalker, Driver reported that “both Han Solo and Leia were way too self-absorbed and into this idea of themselves as heroes to really be attentive parents in the way a young and tender Kylo Ren really needed.”[29] The backstory of how Ben Solo became Kylo Ren was elaborated upon in a prequel graphic novel titled The Rise of Kylo Ren (written by Charles Soule and illustrated by Will Sliney), which was published and released by Marvel Comics from December 18, 2019 to March 11, 2020.[30]

Certain aspects of Kylo Ren's overall arc across the three films of the Sequel Trilogy were also known to Driver from the start of production on the first film. He claimed that he “had one piece of information of where it was all going...and things were building towards that.”[31] He later clarified:

J.J. Abrams told me when I met him for the first time that I should imagine a journey of a character completely opposite to Darth Vader...someone who starts as a child and becomes a man over the course of three movies. He becomes closer to his convictions, becomes more assured about his choices, but has metaphorically and physically killed his father to become his own person.[32] -wikipedia