formidable person; someone not to be taken lightly
Refers to a person of remarkable ability, shrewdness, or presence; often used with a tone of respect or wariness.
He's young, but he's quite a formidable person.
a certain person; someone (unnamed)
Used when referring to a specific person whose name is withheld or unknown; often in narrative or formal contexts.
Information was brought by a certain person.
that sort of person; such a person
Archaic usage; now rarely encountered outside classical or literary texts.
あの新人、ただ者じゃないと思ったら、やはり然る者だった。
I thought that new guy was no ordinary person, and sure enough, he turned out to be someone not to be taken lightly.
It is said that the plan was thwarted by someone (whose name cannot be disclosed).
In old tales, there are many stories of that sort of person appearing and disappearing.
Standard kanji spelling for this expression.
Mixed kana-kanji spelling; commonly seen.
From classical Japanese 然る (saru, 'a certain; such') + 者 (mono, 'person'). The expression is now somewhat literary.