Where does “Блегов” come from?

Блегов (Bulgarian) comes from Romanian bleg, from Proto-Slavic bolgъ — good; nice.

Ancestry of “Блегов”, step by step

Step	Language	Word	Meaning
1	Romanian	bleg	soft, shy, silly, dull, weak, foolish, sheepish;...
2	Proto-Slavic	bolgъ	good; nice