Who said "I have learned that mercy is a luxury of the strong."?

This quote is attributed to Lannister.

I have learned that mercy is a luxury of the strong. - Lannister

"I have learned that mercy is a luxury of the strong."

Lannister Kindness

"A Lannister always pays his debts."

"I am the god of tits and wine."

"You are an awful man."

"I drink and I know things."

"A good man treats his wife with respect."

"Kindness always comes back around."

"The power of a smile can change everything."

"Kindness is weakness to some. Not to me."