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> Ruthenian comes from "Rus", they're the same people.

Russian ethnogenesis is pretty interesting, obscure and politized concept. Especially when you talk about "Rus", because Rus people from chronicals may be (and there is plenty of evidence) Scandinavians, and "Russian" is actually adjective in Russian language, i.e. "someone who belongs to Rus". So, Russians aren't always true East Slavs, especially in modern times.

Although, of course, there is close relationship between eastern Slavic nations, and between them and western Slavs. Southern ones more culturally than ethnically related to other groups (although it is debatable too).