Agency: Doyle Dane Bernbach
As Avis says on its website, "The phrase 'We Try Harder' has gone down in advertising history as one of the longest-lasting and respected taglines. The origination of the slogan was not to create a cute gimmick, but instead it was—and is—a business philosophy that every Avis employee holds true. 'We Try Harder' has helped Avis earn a reputation as one of the most admired businesses in the world."
Source: AdAge.com, Avis.com