Romans 1:16

Οὐ γὰρ ἐπαισχύνομαι τὸ εὐαγγέλιον τοῦ Χριστοῦ· δύναμις γὰρ Θεοῦ ἐστιν εἰς σωτηρίαν παντὶ τῷ πιστεύοντι, Ἰουδαίῳ τε πρῶτον καὶ Ἕλληνι.

RBT Translation:

For I am not ashamed of the Gospel, for she is a powerful one of God into a salvation for everyone who is trusting— both to Caster first and to Greek.

Who are the Greeks?

The ancient Greeks considered themselves to be the most educated and intellectually advanced people in the world (very ethnocentric), particularly during 5-4th century BCE. They were culturally superior to non-Greek-speaking peoples. They were the educated ones. For them, language itself was essentially the marker of intellectual and cultural achievement. It was not about manners or politeness per se, but rather, if you spoke Greek or not. Those who did not know Greek or the Greek customs, they called "barbarian."

Julia Smith Literal 1876 Translation:
For I am not ashamed of the good news of Christ: for it is the power of God to salvation to all believing; both to the Jew first, and the Greek.

LITV Translation:
For I am not ashamed of the gospel of Christ, for it is the power of God to salvation to everyone believing, both to Jew first, and to Greek;