Actors used to have very different, yet standardized, American accents in the earlier part of 20th century cinema.
If you’ve ever seen an American movie from around the 1940s and earlier (and if you’re reading this in the US you probably have), you might have wondered why the performers sound so different from actors today. This video from HowStuffWorks explains the accent, referred to as the Mid-Atlantic or Transatlantic accent:
It’s not just actors from the time period, but also anyone from higher class society at the time: