Who said "I've learned that death is just the end of pain."?

This quote is attributed to Frank Castle.

I've learned that death is just the end of pain. - Frank Castle

"I've learned that death is just the end of pain."

Frank Castle Death

"Punishment is a language they understand."

"I'm not a hero. I'm a tool, sharpened and aimed."

"The only way to stop evil is to be better at it than they are."

"Mercy is for the living. The dead don't care."

"Death doesn't scare me anymore."

"Death and I are old friends."

"Welcome to my world."

"Death is just the beginning."