Star Wars: The Rise of Skywalker director J.J. Abrams says Finn's origin will be addressed in the film. Introduced as one of the sequel trilogy's three main heroes in The Force Awakens (along with Rey and Poe Dameron), Finn is arguably one of the more interesting characters in the saga. As many fans know, he started as a First Order stormtrooper and eventually defected. Initially, Finn's goal was to run far away from the war, but through his experience with Rose in The Last Jedi, he's now a dedicated member of the Resistance and doing everything he can to fight against the tyranny of the First Order.
The Force Awakens makes a point to mention Finn had no prior incidents of "non-conformity" before the movie's events, and General Hux tells Kylo Ren his stormtroopers are programmed from birth to serve. With that in mind, it was curious why Finn had such a change of heart and left the First Order behind. Some viewers assumed there had to be more to the story, and it sounds like The Rise of Skywalker is going to have some revelations about the former FN-2187.
Speaking with Vanity Fair, Abrams mentioned that The Rise of Skywalker will indeed cover more of Finn's past, providing further insight into the character and answering some lingering questions viewers might have had:
“It is part of the story of this one. And it was alluded to in Episode VII, but there’s a bit more light shed on that in this one... I would say that each of the characters get more light shed on their histories. I’m not saying we get full, exhaustive downloads on all of their childhoods and every major step that got them to where they are. But there are a lot of questions about Finn’s past, about Poe’s past, obviously Rey and Kylo, and then some of the new characters we meet.”
All the sequel trilogy's revealed about Finn's backstory to date is that he was taken away from his family, who he doesn't know. It's difficult to say how The Rise of Skywalker can add to this, considering how spoiler-averse official marketing materials are. The various trailers and TV spots provide precious few clues about the film's actual narrative, primarily showing Finn partaking in various action sequences like the Pasaana speeder chase. As such, it's anyone's best guess what Abrams has up his sleeve, but hopefully The Rise of Skywalker fleshes Finn out and helps paint a more complete picture of his overall arc. Rey and Kylo Ren are (understandably) the main focus of the trilogy, but Finn's just as much of an essential player. It's nice that Abrams didn't leave Finn behind and made sure to give the old stormtrooper his due.
Perhaps further details about Finn's backstory are connected to one of the new characters The Rise of Skywalker introduces, such as the First Order's Allegiant General Pryde or freedom fighter Jannah. It's already been confirmed Keri Russell's Zorii Bliss is someone who has a history with Poe, explaining her role in the story. That shows Abrams was thinking about ways he could intertwine the returning characters with the newcomers to bring everything together. For what it's worth, Pryde worked with Hux to create the First Order's army of stormtroopers, so it's reasonable to assume Pryde could be the new Captain Phasma and have ties to Finn.
Source: Vanity Fair