expression, noun
a certain person; a certain amount
A set phrase used to refer vaguely to an unspecified person or amount, often with a dismissive or humble tone. The meaning depends on context: when referring to a person, it implies 'somebody or other'; when referring to an amount, it implies 'some amount or other'. The phrase is somewhat old-fashioned and literary.
何の某という者が訪ねてきたが、名を聞きそびれた。
Somebody or other came to visit, but I missed asking their name.
彼は何の某の金を寄付したそうだ。
I heard he donated some amount of money or other.
某 alone can mean 'a certain person' or 'a certain amount', but 何の某 is a more emphatic and literary set phrase.
誰某 is a more common and modern way to say 'somebody or other', while 何の某 is rarer and more literary.
The phrase combines 何の (what kind of) with 某 (a certain person/amount), forming a literary expression for an unspecified person or amount. The exact historical derivation is uncertain.