Ruthenian and Ruthene are exonyms of Latin origin, formerly used in Eastern and Central Europe as common ethnonyms for East Slavs, particularly during the late medieval and early modern periods.

The Latin term Rutheni was used in medieval sources to describe all Eastern Slavs of the Grand Duchy of Lithuania, as an exonym for people of the former Kievan Rus', thus including ancestors of the modern Belarusians, Rusyns and Ukrainians.

[12][13] Ruteni, a misnomer that was also the name of an extinct and unrelated Celtic tribe in Ancient Gaul,[7] was used in reference to Rus in the Annales Augustani of 1089.

[7] An alternative early modern Latinisation, Rucenus (plural: Ruceni) was, according to Boris Unbegaun, derived from Rusyn.

[14][15]According to professor John-Paul Himka from the University of Alberta the word Rutheni did not include the modern Russians, who were known as Moscovitae throughout Western Europe.

[7][16] Vasili III of Russia, who ruled the Grand Duchy of Moscow in the 16th century, was known in European Latin sources as Rhuteni Imperator.

[18][19] Professor David Frick from the Harvard Ukrainian Research Institute has also found in Vilnius the documents from 1655, which demonstrate that Moscovitae were also known in Lithuania as Rutheni.

[20] The 16th century Portuguese poet Luís Vaz de Camões in his Os Lusíadas" (Canto III, 11)[21][22] clearly writes "...Entre este mar e o Tánais vive estranha Gente: Rutenos, Moscos e Livónios, Sármatas outro tempo..." [English translation: "...Between this sea and the Tánais live strange People: Ruthenians, Muscovites and Livonians, Sarmatians in another time..."] differentiating between Ruthenians and Muscovites.

After the partition of Poland, the term Ruthenian referred exclusively to people of the Rusyn- and Ukrainian-speaking areas of the Austro-Hungarian Empire, especially in the Kingdom of Galicia and Lodomeria, Bukovina, and Transcarpathia.

[7] At the request of Mykhailo Levytsky, in 1843, the term Ruthenian became the official name for the Rusyns and Ukrainians within the Austrian Empire.

During the early 20th century, the name Ukrajins'ka mova ("Ukrainian language") became accepted by much of the Ukrainian-speaking literary class in the Austro-Hungarian Kingdom of Galicia and Lodomeria.

After several years, the Rusyn and Ukrainian speaking areas of eastern Austria-Hungary found themselves divided between the Czechoslovakia, Poland, and Romania.

When commenting on the partition of Czechoslovakia by Nazi Germany in March 1939, US diplomat George Kennan noted, "To those who inquire whether these peasants are Russians or Ukrainians, there is only one answer.

[26] Ruthenians who identified under the Rusyn ethnonym and considered themselves to be a national and linguistic group separate from Ukrainians and Belarusians were relegated to the Carpathian diaspora and formally functioned among the large immigrant communities in the United States.

[7] Since the 19th century, several speculative theories emerged regarding the origin and nature of medieval and early modern uses of Ruthenian terms as designations for East Slavs.

On those bases, an entire strain of speculative theories was created, regarding the alleged connection between ancient Gallic Ruthenes and later East Slavic "Ruthenians".

The eastward expansion of the Grand Duchy of Lithuania had been facilitated by amicable treaties and inter-marriages of the nobility when faced with the external threat of the Mongol invasion of Kievan Rus'.

One and a half years after the Union of Krewo, the Wilno (Vilnius) episcopate was created which received a lot of land from the Lithuanian dukes.

By the mid-16th century Catholicism became strong in Lithuania and bordering with it north-west parts of White Ruthenia, but the Orthodox church was still dominant.

Gregory's canonical territory was the western part of the traditional Kievan Rus' lands — the states of the Grand Duchy of Lithuania and the Kingdom of Poland.

The formation of the church led to a high degree of confrontation among Ruthenians, such as the murder of the hierarch Josaphat Kuntsevych in 1623.

Opponents of the union called church members "Uniates", although Catholic documents no longer use the term due to its perceived negative overtones.

Domination of tsarist-ruled Ukraine by the Russian Empire (from 1721) eventually led to the decline of Uniate Catholicism (officially founded in 1596) in the Ukrainian lands under Tsarist control.Musical scores titled "Baletto Ruteno" or "Horea Rutenia", meaning Ruthenian Ballet can be found in European collections during the Lithuanian and Polish rule of Ruthenia, such as the Gdańsk lute tablature of 1640.