Who said "Death is not the end—it is merely a transformation."?

This quote is attributed to Sif.

Death is not the end—it is merely a transformation. - Sif

"Death is not the end—it is merely a transformation."

Sif Death

"I have waited lifetimes for this moment."

"A warrior's heart beats strongest in battle."

"We are bound by more than just duty."

"The past shapes who we become."

"Death doesn't scare me anymore."

"Death and I are old friends."

"Welcome to my world."

"Death is just the beginning."