Where does “Шерлок” come from?

Шерлок (Russian) comes from English Sherlock, from Old English scir-lock — bright-lock.

Ancestry of “Шерлок”, step by step

Step	Language	Word	Meaning
1	English	Sherlock	To deduce; To search; To obsolete a unique...
2	Old English	scir-lock	bright-lock