The longer explanation:
There is three kinds of "Russians". Rus`, Rusyns, Russians.
Rus` lived at Baltic Sea. Rus` means "red". They were warriors, i.e. their life was to fight, trade, and collect taxes. Their native language is unknown (probably, Old Norse). At times of Great Epidemic, they left their city (now known as Old Russa, Старая Русса) and "concurred" South and started to govern it, so territory of current Ukraine got name "Rus`". Slavish colonists at these territories got name "Rusyns" (русины) (see below). At time of expansion of Rus`, North people was concurred and paid taxes to Rus` (Лаврентеевская летопись, ст 4. об. «А вот другие народы, дающие дань Руси: чудь, меря, весь, мурома, черемисы, мордва, пермь, печера, ямь, литва, зимигола, корсь, нарова, ливонцы, - эти говорят на своих языках, они - потомство Иафета, живущее в северных странах.»). They got name "Russish" (русские). This was time of "Great Rus`", so North Russians are also known as "Great Russians" (Великоросы), while South Russians (Slavs) are also known as "Little (Core) Russians" (Малоросы).
Summary:
* Rus` - possibly warriors union or Varangians, native language (probably): Old Norse.
* Rusyns (Ukrainians) - Slavish colonists governed by Rus`, native language: Slavish.
* Russish (Russians) - native Europeans, native language: many, probably Finno-Ugric and others.
https://en.wikipedia.org/wiki/Rus'_peoplehttps://en.wikipedia.org/wiki/Varangians
https://en.wikipedia.org/wiki/Staraya_Russa
https://en.wikipedia.org/wiki/Ruthenia
https://en.wikipedia.org/wiki/Rus'_%28name%29#From_Rus.27_to...
https://en.wikipedia.org/wiki/Finno-Ugric_peoples
NOTE: -in, -yn, -an means "he/she" (modified "он" - "he"), -yny, -iny, -any, -ini, etc. - "they" (modified "они" - they) ("y" as in lynx). So Rysyn (русин) means "he is Rus`", Rysyny (русини) means "they are (people of) Rus`". Russians means "they are Russia", "россияне", but selfname of Russians is Russish ("русские").
Moreover, Russia is Greek name of Rus`, given by Catherine II (born in Prussia) to Moscovia, because Russia was used at West as name of past parts of Great Russia. Nikolai Kostomarov wrote something like "LOL, we are Russians now" at time of rename (ДЂло въ томъ, что названіе Руси укрЂпилось издревле за южнорусскимъ народомъ. Названіе не возникаетъ безъ факта. Нельзя навязать народу ни съ того, ни съ сего какое-нибудь имя. Это могло приходить въ голову только такимъ мудрецамъ, противъ которыхъ мы недавно писали (1) и которые намъ сообщили прекурьёзную новость, какъ Екатерина II, высочайшимъ повелЂніемъ, даровала Московскому народу имя Русскаго и запретила ему употреблять древнее свое имя — Московитяне.)