Synonymous

There are many alternate worlds, and quite a few Ways between them. The odds of finding another being in another world that's functionally identical to you are very low... but not zero. These improbably copies are referred to as Synonyms or Synonymous "____" with the blank being the name of the original version from your world.

The usual etiquette is to refer to a Synonymous person as Synonymous Gregg or what have you although people will often refer to Synonymous animals as Synonymous Rats or what have you.

TRIVIA -the otherworldly rat creatures in the New York Subway System expressly say they are not Synonymous, implying they're just very similar creatures.