These are the 10 groups of peoples with distinct regional, ethnic or religious identities that have influenced the Lithuanian nation the most and left the most heritage within Lithuania:
1.Lutherans. For centuries Lithuania was divided into two distinct sub-ethnic areas: the east, ruled by Poland-Lithuania and then Russia, remained Catholic, while the west (ruled by Germans) became Lutheran. That Lutheran Lithuania, or Lithuania Minor, was destroyed by the Soviet genocide after World War 2 and Lutheran percentages there dwindled from ~95% to under 5%. However, much heritage still reminds this unique community born at the crossroads of Lithuanian and German cultures. This includes red brick churches and buildings, talented metalworks and more. Lutherans make up 0,7% of Lithuania's population.
2.Poles. A centuries-old alliance and then federation between Poland and Lithuania caused many Lithuanians (~10%) to adopt Polish language and culture over generations. These "Poles-Lithuanians" greatly influenced the wider Polish culture, creating many great works of art and literature in Lithuania and beyond, as well as wielding massive political influence. Most of them had both Polish and Lithuanian versions of their names and, after the Polish and Lithuanian nations have completely separated after World War 1, it became often disputed whether they were "mainly Poles" or "mainly Lithuanians". During 19th-20th centuries many "Polish-Lithuanians" switched back to Lithuanian language and customs, but perhaps just as many opted for a singular Polish identity. As such, two Lithuanian municipalities (out of 60) currently have Polish majorities (the Poles are concentrated around Vilnius). Poles make up 6,65% of Lithuania's population.
3.Pagans. Lithuania was the final independent nation of Europe to abandon paganism. Some may claim it was never fully abandoned at all, as many pagan practices remained within now-Christian festivals. These days, however, thousands of people seek to restore the full pagan faith as well, starting the neo-pagan Romuva religion. They were extremely successful and Romuva became the fastest growing faith in Lithuania, quadrupling its followers between 2001 and 2011 censae. They have constructed prehistory-inspired holy sites (alkas) where they celebrate the once-dying-out festivals. Pagans make up 0,2% of Lithuania's population.
4.Samogitians. While Lithuania is divided into 5 sub-ethnic regions, Samogitia is the one that clings to its unique identity the most. Samogitian dialect is so distinct that it is sometimes considered a separate language, and a few Samogitians even claim "Samogitian" rather than "Lithuanian" as their ethnicity in censae. To others, Samogitians are the "best Lithuanians", as they were the only ones that even had their nobility speaking Lithuanian through all the centuries (rather than adopting more politically convenient Polish, German or Russian). Approximately 17% of Lithuania's population live in Samogitia, most of them natively Samogitians.
5.Jews. The numbers of Lithuania's Jews peaked in the 19th century when Lithuania was among the few lands of Russian Empire where they were allowed to freely settle. While later emigration and genocide have dwindled their numbers, the Jewish heritage in Lithuania is still impressive, consisting of some 80 synagogues and memories of key Jewish figures who have influenced the Jewish thought worldwide, such as Vilna Gaon. Jews make up 0,1% of Lithuania's population.
6.Karaims are a unique ethnoreligious group following a religion that includes some Jewish, Christian and Islamic practices. Their ancestors were brought in from southernmost reaches of Grand Duchy of Lithuania by grand duke Vytautas. Today however even in their original homeland there are just 1000 or so left, so the Karaim communities of Lithuania with their two kenessas (temples) have few counterparts in the world. While Karaim faith seems exotic, Karaim cuisine (kibin pasties) is popular among people of Lithuania of all ethnicities. Karaims make up 0,01% of Lithuania's population, numbering just around 250.
7.Lithuanian Americans. The USA was the favorite destination of Lithuanian migrants, especially during times of occupations. During periods of independence (1918-1940, 1990-) some Lithuanian-Americans have returned to Lithuania to help reestablish its economy and political system. They have wielded a disproportionate influence. Some have bequeathed their riches and works of art to Lithuania, creating numerous museums in Lithuania. Lithuanian-Americans have also popularized basketball in Lithuania. There are some 700 thousand people of Lithuanian ancestry in the USA. If they would all migrate to Lithuania, they would make up 19% of population
8.Russian Old Believers descend from Russian Orthodox people who refused to adhere to Nikon's reforms centuries ago. As a result, they became heavily persecuted in Russia and sought refuge in 17th century Lithuania. Heavily guarding their identity and "true faith" they established many out-of-the-beaten-path villages centered around pretty wooden churches in the Lithuanian countryside. Many now are empty, but their churches and cemeteries come to life once again when the Old Believers come from the cities for religious festivals. Old Believers make up 0,9% of Lithuania's population.
9.Muslim Tatars. As Lithuania was at its largest extent in the 15th century, it even ruled part of the Islamic world near the Black Sea. From there the Grand Duke Vytautas has brought in thousands of Tatars and hired them as soldiers. Over the centuries they have lost their language but not their religion, which has developed some unique characteristics. While Tatar numbers dwindled through assimilation, a few wooden mosques remained as an interesting addition to Lithuanian countryside. Lithuanians also enjoy the Tatar cuisine (čeburekai pasties, šimtalapis cake). Muslim Tatars make up 0,1% of Lithuania's population, of them some half with Medieval origins.
10.Soviet settlers. Arguably the most controversial community of Lithuania, the Soviet settlers are largely Russophone people sent to live in Lithuania by the Soviet Union (and their descendants). Being mostly urban, they add a "Russian" touch to Lithuanian cities, making the Russian music, festivals and media more popular. Some third of them emigrated after the Soviet Union collapsed, and the new generations tend to slowly integrate. Soviet settlers and their descendants make up ~6% of Lithuania's population.
Note: the list above is subjective and it is meant to serve just as an introduction of the key minorities of Lithuania. For an objective and extensive articles on all the Lithuania's ethnic and religious groups, please see the sections on Ethnicities of Lithuania and Religions of Lithuania.