Definition of goodwill ambassador in US English:

goodwill ambassador

noun

  • A person serving (usually unofficially) to promote goodwill between countries, institutions, etc.; now chiefly (frequently with capital initials) a well-known person (especially a celebrity) appointed by a charity or other organization to publicize its activities or promote a specified cause.

Origin

1920s; earliest use found in Kokomo (Indiana) Daily Tribune.