The Karelian language is similar to Finnish. It was Scandinavian sources that first mentioned the Karelians. They were such a menace to the Vikings in the 600s that the Swedes founded Stockholm for protection from Karelian raids. Russian sources did not mention them till 1143.
There were efforts by both Eastern Orthodox and Roman Catholics to Christianized them in the 1100s-1200s, but these failed. They finally became Orthodox in the 1600s, but they were often caught between the Russians who wanted them Orthodox and the Swedes who wanted them Protestant.
Most live either in Russia or Finland, but smaller numbers live in Belarus, Ukraine or Kazakhstan. They are least reached with the gospel in Ukraine and Kazakhstan.

Karelians in Russia are becoming Russified. They are in the process of losing their language and culture. In other countries they retain their language, though they also speak the trade language.

Most Karelians are Christian, but like many people in Europe and Russia, they often have a secular worldview. Many do not accept the Bible as God’s final word or believe Jesus Christ is the only way to salvation. They have varied ideas about the afterlife, many of which conflict with the Bible.

Karelians need a Christ-centered theology and a willingness to accept his lordship.

Pray for Karelian families to be abundantly blessed by the Lord, leading others to find hope in Jesus Christ.
Pray for Karelian disciples who will make more disciples who will make even more disciples.
Pray that soon there will be Karelian workers who will take the name of Christ to others.

Scripture Prayers for the Karelian, Norgorod in Russia.

https://en.wikipedia.org/wiki/Karelians