The first non-American actress to play Wonder Woman. In contrast to other trends, though, they did not choose a British actress to play an American hero(ine)*. This does not seem a gag pace Peter Sellers as Nayland Smith or Woody Allen in 1967 or George Segal as Sam Spade or Elliot Gould as Philip Marlowe.
*Does Wonder Woman have US citizenship? I would say no, since as Princess Diana she still has her title of nobility, I suppose. One may not keep such a title as a U.S. citizen.