A thread on important Turkish Christians in history.
Some of their ethnicities might be ambiguous, for example, I did not include St. John of Konitsa since sources said he was an Albanian. If there's a mistake in this thread please forgive me, Source: Pastor Marc Madrigal's book

Rabban Bar Sauma was an Ongud Turk who was part of the Church of the East in the 13th century. He's a monastic turned diplomat and traveled from China to France, visiting Constantinople and Rome. After returning back to his homeland, the inverse Marco Polo wrote about his travels

Simon Osman (Atumano) was a 14th century Turkish convert to Catholicism. His father was Turkish while his mother was Roman.
While he was Orthodox in the Studion Monastery, he converted to Catholicism due to Barlaam and was his successor as a bishop. He spoke and Latin

Schemamonk Nicholas “Yusuf Amptnoul Ogly” was a 19th-century Turkish pasha who converted to Orthodox Christianity. He was tortured for betraying Islam and managed to flee to Kazan, he was tonsured to become a schemamonk, his life is very similar to St. Andrew of Constantinople.

Holy Martyr St. "Hoca Emir" Tounom (Feast day April 18 NC) was an Ottoman Emir, after witnessing the Holy Fire miracle he converted to Orthodox Christianity. His Turkish "friends" found out about it and tortured him until death. https://www.johnsanidopoulos.com/2010/04/saint-tounom-omir-18-april-1579.html

Holy New Martyr St. Nicholas Karaman of Smyrna (Feast Day December 5th) was a Turkish Orthodox Christian. He was brought to a Kadi (Judge) and was asked if he would embrace Islam. Nicholas rejected in spite of many requests. He was tortured and hanged for his Christian faith.

Holy Martyr St. Ahmet (May 3rd) was a Turkish government official. After witnessing the Divine Liturgy in the Ecumenical Patriarchate he converted to Orthodox Christianity. His fellow "compatriots" found out about his conversion, he was tortured and martyred for his faith

St Daniel "Musa Ahmetoglu" (18th c.)converted to Orthodoxy after witnessing the martyrdom of St. Anastasius of Epirus. He wanted to be martyred but he was dissuaded by patriarch Sophronios of Jerusalem. He became a monk and founded a church in Paramythia in St. Anastasius' honor.

St. Constantin of Mytilene was a 19th Century Turkish Muslim. After living a life of degeneracy, he repents and meets patriarch Gregory V in Mt. Athos and is baptized by him. Being found out by his "compatriots", he was tortured and martyred for his faith. https://www.johnsanidopoulos.com/2015/06/holy-new-martyr-constantine-former.html

Of course this thread could be expanded if we were to include the Gagauz Saints.
The Chuvash, Gagauz, Pecheneges, Karaman's, Yakuts Western Cumans all had a sizable Christian population
There was a Pecheneg Orthodox Church in the 12th century thanks to Kurya Kaan.

Western Cumans converted to Catholicism in the 13th century and even had their own diocese for a short while https://en.wikipedia.org/wiki/Roman_Catholic_Diocese_of_Cumania
Codex Cumanicus gives us an insight on the Lord's prayer in the Cuman language: