Where does “Mithras” come from?

Mithras (Latin) comes from Ancient Greek Μίθρας, from Proto-Iranian Miθra.

Ancestry of “Mithras”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	Μίθρας	—
2	Proto-Iranian	Miθra	—

Mithras — Etymology, Origin & Word History | Etymology Explorer