Leia (aka Resistance leader General Organa) tells Han that Snoke was the one who corrupted their son Ben
into becoming Kylo Ren
From Alan Dean Foster novelization:
First we have Maz discussing Snoke with Han:
“I need you to get this droid to the Resistance…,” Han said.
“Me?” Maz said archly.
“…and the loan sounds good too.”
“I see you’re in trouble,” Maz said. “I’ll help you find passage—avoid Snoke’s hunter squads — but this journey to the Resistance isn’t mine to take, and you know it.”
And then Leia's chat with him
“We both did,” Leia admitted.
He met her eyes steadily. “We’ve lost our son, forever.”
Leia bit her lower lip, refusing to concede. “No. It was Snoke".
She even admits she knew this for a long time - so this knowledge isn't merely from the year The Force Awakening is in:
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.