The Russians share many cultural traits with their fellow East Slavic counterparts, specifically Belarusians and Ukrainians. They are predominantly Orthodox Christians by religion. The Russian language is official in Russia, Belarus, Kazakhstan, Kyrgyzstan, and Tajikistan, and also spoken as a secondary language in many former Soviet states.
There are two Russian words which are commonly translated into English as "Russians". One is "русский" (russkiy), which most often means "ethnic Russians". Another is "россияне" (rossiyane), which means "citizens of Russia". The former word refers to ethnic Russians, regardless of what country they live in and irrespective of whether or not they hold Russian citizenship. Under certain circumstances this term may or may not extend to denote members of other Russian-speaking ethnic groups from Russia, or from the former Soviet Union. The latter word refers to all people holding citizenship of Russia, regardless of their ethnicity, and does not include ethnic Russians living outside Russia. Translations into other languages often do not distinguish these two groups.
The name of the Russians derives from the Rus' people (supposedly Varangians). According to the most prevalent theory, the name Rus', like the Finnish name for Sweden (Ruotsi), is derived from an Old Norse term for "the men who row" (rods-) as rowing was the main method of navigating the rivers of Eastern Europe, and that it could be linked to the Swedish coastal area of Roslagen (Rus-law) or Roden, as it was known in earlier times. The name Rus' would then have the same origin as the Finnish and Estonian names for Sweden: Ruotsi and Rootsi. According to other theories the name Rus' is derived from Proto-Slavic *roud-s-ь ( from *rъd-/*roud-/*rуd- root), connected with red color (of hair) or from Indo-Iranian (ruxs/roxs — «light-colored», «bright»).
The modern Russians formed from two groups of East Slavic tribes: Northern and Southern. The tribes involved included the Krivichs, Ilmen Slavs, Radimichs, Vyatiches and Severians. Genetic studies show that modern Russians do not differ significantly from Belarusians and Ukrainians. Some ethnographers, like Zelenin, affirm that Russians are more similar to Belarusians and to Ukrainians than southern Russians are to northern Russians. Russians in northern European Russia share moderate genetic similarities with Uralic peoples, who lived in modern north-central European Russia and were partly assimilated by the Slavs as the Slavs migrated northeastwards. Such Uralic peoples included the Merya and the Muromians.
Outside archaeological remains, little is known about the predecessors to Russians in general prior to 859 AD when the Primary Chronicle starts its records. It is thought that by 600 AD, the Slavs had split linguistically into southern, western, and eastern branches. The eastern branch settled between the Southern Bug and the Dnieper Rivers in present-day Ukraine; from the 1st century AD through almost the turn of the millennium, they spread peacefully northward to the Baltic region, forming the Dregovich, Radimich and Vyatich Slavic tribes on the Baltic substratum, and therefore experiencing changed language features such as vowel reduction. Later, both Belarusians and South Russians formed on this ethnic linguistic ground.