Who said "The end is the only constant."?

This quote is attributed to Thanos.

The end is the only constant. - Thanos

"The end is the only constant."

Thanos Death

"I am inevitable."

"The hardest choices require the strongest wills."

"Perfectly balanced, as all things should be."

"You should have aimed for the head."

"Death doesn't scare me anymore."

"Death and I are old friends."

"Welcome to my world."

"Death is just the beginning."