Where does “Кирилл” come from?

Кирилл (Russian) comes from Ancient Greek Κύριλλος, from Ancient Greek κῡ́ριος.

Ancestry of “Кирилл”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	Κύριλλος	—
2	Ancient Greek	κῡ́ριος	—

Кирилл — Etymology, Origin & Word History | Etymology Explorer