Who said "The greatest riddle is not external—it is the self"?

This quote is attributed to Riddler.

The greatest riddle is not external—it is the self - Riddler

"The greatest riddle is not external—it is the self"

Riddler Solitude

"Riddles are the most honest form of communication - they demand truth wrapped in mystery."

"A mind that cannot solve a puzzle is a mind that cannot live."

"Questions are the doorway to knowledge, answers are merely the threshold."

"The greatest riddle is why people fear enlightenment."

"Sometimes being the best means being the loneliest."

"Solitude gives us time to reflect on what matters"

"I'm not good with people, never have been."

"I feel like I'm disappearing."