expression, noun
person of doubtful origin; nobody
Derogatory set phrase used to dismiss someone as having no respectable background or credentials. Often appears in the pattern どこの馬の骨ともわからない (some nobody from who-knows-where).
どこの馬の骨ともわからない男に娘をやれるか。
How could I give my daughter to some nobody from who-knows-where?
彼は「あんな馬の骨に任せられるか」と怒った。
He got angry, saying, 'How could we leave it to a nobody like that?'