Who said "Your journey to the dark side is complete."?

This quote is attributed to Palpatine.

Your journey to the dark side is complete. - Palpatine

"Your journey to the dark side is complete."

Palpatine

"Did you ever hear the tragedy of Darth Plagueis the Wise?"

"The dark side of the Force is a pathway to many abilities some consider to be unnatural."

"Have you ever heard of the tragedy of Darth Plagueis? I thought not."

"Unlimited power!"