Who said "I'm not a quitter. That's not in my vocabulary."?

This quote is attributed to Snoopy.

I'm not a quitter. That's not in my vocabulary. - Snoopy

"I'm not a quitter. That's not in my vocabulary."

Snoopy Perseverance

"I think I'm dying. Send for a doctor immediately!"

"Rats! Another day, another disappointment."

"Sometimes I lie awake at night and ask, 'Is life a multiple choice test or an essay?' Then a dog barks and I realize it doesn't matter."

"I love mankind. It's people I can't stand."

"Perseverance is the key to success."

"Don't give up on what you believe in."

"I've been through worse."

"You learn to live with the pain."