Ruteni
Ruteni is a term that can refer to several entities, primarily a historical Slavic people and a modern administrative division in Ukraine. Historically, the Ruthenians were a group of East Slavic tribes who inhabited the territories of modern-day Western Ukraine, parts of Eastern Poland, Slovakia, and Romania. They were closely related to other East Slavic groups, including the ancestors of modern Russians and Belarusians. The term "Ruthenian" was commonly used in Western European sources from the Middle Ages onwards to refer to these East Slavic populations.
Over time, the political and social landscape of the region led to the differentiation of these groups.