Who said "Death is life's final, unsolvable riddle"?

This quote is attributed to Riddler.

Death is life's final, unsolvable riddle - Riddler

"Death is life's final, unsolvable riddle"

Riddler Death

"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."

"Death doesn't scare me anymore."

"Death and I are old friends."

"Welcome to my world."

"Death is just the beginning."