When did Ben Solo fall to the dark side?
As of Claudia Gray’s canon novel Bloodline, Ben Solo is approximately 23 years old and still believed to be travelling with his uncle Luke as a Jedi apprentice. His mother cannot make contact with him in the novel, so his true status at the time of the novel’s events is unknown (i.e. we only know what Leia believes to be the case). Therefore, Ben either turned very close to the events of the novel or in the aftermath of them.
Who was responsible for Ben Solo’s fall?
This is unclear, but the answer would appear to be some combination of 1. Snoke and 2. Ben himself.
How was Ben Solo seduced to the dark side?
Information on the circumstances of Ben Solo’s fall is currently lacking, but the best place to start is probably the film itself:
There was nothing we could’ve done. There was too much Vader in him.
That’s why I wanted him to train with Luke. I just never should have sent him away. That’s when I lost him. That’s when I lost you both.
We both had to deal with it in our own way. I went back to the only thing I was ever good at.
We both did.
We lost our son, forever.
No. It was Snoke. He seduced our son to the dark side. But we can still save him. Me. You.
Two potential explanations are raised here, one from each parent: Han evidently believes Ben was pre-disposed to the dark side (“there was too much Vader in him”), whereas Leia places the blame more on Snoke’s shoulders (“he seduced our son to the dark side”).
These ideas were elaborated on in the behind-the-scenes documentary Secrets of The Force Awakens (found as a special feature on the blu-ray). Director J.J. Abrams commented that:
“It’s more than just having a ‘bad seed’ as a kid. Snoke had targeted this kid and knew that this kid was going to be incredibly powerful in The Force and wanted him as an ally. So this mother and father had a target as a son, someone who’s watching their boy, and these parents aren’t there enough to guide him.”
This, then, would suggest that the director is more inclined to trust Leia’s take (that Snoke engineered Ben’s fall) than Han’s (that there was just some innate evil in the boy). This is further reinforced by the novelisation of The Force Awakens by Alan Dean Foster, which provides an extended version of Han and Leia’s conversation about Ben:
He met her eyes steadily. “We’ve lost our son, forever.”
Leia bit her lower lip, refusing to concede. “No. It was Snoke.”
Han drew back slightly. “Snoke?”
She nodded. “He knew our child would be strong with the Force. That he was born with equal potential for good or evil.”
“You knew this from the beginning? Why didn’t you tell me?”
She sighed. “Many reasons. I was hoping that I was wrong, that it wasn’t true. I hoped I could sway him, turn him away from the dark side, without having to involve you.” A small smile appeared. “You had—you have—wonderful qualities, Han, but patience and understanding were never among them. I was afraid that your reactions would only drive him farther to the dark side. I thought I could shield him from Snoke’s influence and you from what was happening.” Her voice dropped. “It’s clear now that I was wrong. Whether your involvement would have made a difference, we’ll never know.”
He had trouble believing what he was hearing. “So Snoke was watching our son.”
“Always,” she told him. “From the shadows, in the beginning, even before I realized what was happening, he was manipulating everything, pulling our son toward the dark side. But nothing’s impossible, Han. Not even now, at this late time. I have this feeling that if anyone can save him—it’s you.”
This elaborated version is interesting because it presents a more complicated picture, suggesting that Leia discovered that Snoke had been influencing Ben from infancy and tried to deal with the situation by herself without explaining what was happening to Han. This secretiveness would appear to have only compounded the problem, convincing Han that his son turned because of his innate evil rather than a malign outside influence.
This, of course, leaves one main area uncovered – how Ben himself felt as a child and young adult. Actor Adam Driver, in the Secrets of the Force Awakens documentary, made the following comments:
“If you really imagine the stakes of him, in his youth, having all these special powers and having your parents kind of be absent during that process on their own agendas, [being] equally as selfish. He’s lost in the world that he was raised in, and feels that he was kind of abandoned by the people that he’s closest with. He’s angry because of that, I think, and he has a huge grudge on his shoulders.”
So, while his parents – particularly his mother – tried to do their best for him, despite leading busy lives and having other concerns, it would seem that the move that was meant to help him – sending him to his uncle – only compounded the feelings of abandonment and rejection that made him vulnerable to Snoke’s temptation.