It also brought back one of Han’s most iconic lines. When his son struggles to say the words “I love you” to him, Ford’s character replies to the silence with: “I know …” That’s the same thing he told Leia, the young man's mother, when she said those words to him in The Empire Strikes Back.

Screenwriter Chris Terrio emphasized that what the audience sees is in Ren's head, not a Force ghost. Solo appears only after Leia uses the Force from across the galaxy to awaken the good side of her child, the Ben Solo who was extinguished, before she fades away herself.

“At least for J.J. and I, we thought that this finally was Ren, after the death of his mother, being able to really ask for forgiveness, to ask his father for forgiveness, and make some kind of peace,” Terrio said. “He cannot go back and take back what he has done to his father, but as Han says, ‘Your mother's gone but what she stood for and what she fought for, that's not gone," so he still can make amends in the future.”

Abrams told Ford it was vital "to have him be in that scene, to have Kylo get to dramatize the thing that he'd been playing some form of [in his head].”

This was foreshadowed by a line earlier in the movie, when Rey tells Ren: “I see through the cracks in your mask. You’re haunted. You can’t stop seeing what you did to your father.”

“[Ren] was sort of suppressing and rejecting what he had done,” Abrams said, invoking a line the young villain said in writer-director Rian Johnson’s previous installment The Last Jedi: Kill the past.

“Why do you think he wants to kill the past? It's like there's this thing that is haunting him. It's not until he's shown compassion by Rey that he allows himself to have that conversation,” Abrams said. “It’s the thing that will crush him, and the idea that he knows the spirit of his father would give him permission and encouragement to go to the light side.”

After directing him as Solo the first time, Abrams talked about the emotion of seeing Ford reprise the character. It was just as emotional seeing him do it for the last time. “When we were doing The Force Awakens I couldn’t— and I still can’t —imagine what it would be like to come back at that point, nearly 40 years later, and wear a costume and play a character again. I just think it's insane, for all of them, not just for Harrison.”

Abrams, who had thought he would be one-and-done with Star Wars after that earlier film, found himself bonding in a new way with Ford on Episode IX. “It was weird to be on the Star Wars set and to share with Harrison the feeling of ‘I never thought I'd be back here doing this,’” Abrams said. “Of course his experience was far greater than mine in every way, but it was beautiful having him there with Adam. The two of them always had a great sort of spark. They somehow gave each other permission, not literally before the scene but just their nature, to be open and be so vulnerable.”

Han Solo is an emotional touchstone for people who grew up adoring the original trilogy, so Abrams said Ford’s return was an emotional catalyst not just for Kylo Ren but for longtime Star Wars fans, too.

“To see two characters that are these traditionally pretty tough guys be so vulnerable to me speaks to the beauty of what Star Wars has always been,” Abrams said. “Star Wars was always a story of the underdog and this inclusive sort of world where anyone, organic or synthetic, male or female, doesn't matter what your race or species, it's an equal opportunity place. So I just love having these two men not behaving in a way that you'd necessarily expect to see either of them... And of course having Han get to pay off the "I know" with his son, that was incredibly touching.”

Terrio added that Driver sprinkled various Harrison Ford elements throughout his own performance in the film, from the way he points in the face of General Hux, to the way he fires a blaster over his shoulder without looking, and finally the little open-handed shrug he gives the Knights of Ren before their last battle.

"That was actually a very conscious thing that J.J. and Adam talked about," Terrio said. "There could be subtle ways for you to see the ghost of Ben Solo in there somewhere, just his physicality. There are certain things like that in the movie that I see which I'm pretty convinced are Adam showing you what Ben Solo would have looked like before by showing what he inherited from his father."