Who said "Gratitude is strength, not weakness."?

This quote is attributed to Hulk (The Avengers).

Gratitude is strength, not weakness. - Hulk (The Avengers)

"Gratitude is strength, not weakness."

Hulk (The Avengers) Gratitude

"Puny god."

"You want a Hulk? You're looking at a Hulk right now."

"I'm always angry."

"That's my secret, Captain. I'm always angry."

"Gratitude makes life richer."

"A grateful heart is a happy heart."

"Respect those who came before us."

"Life's greatest treasures are the people we love"