hard to replace (with another person); irreplaceable (person)
Fixed expression meaning that a particular person is so valuable or unique that no one else can take their place. Often used in formal or written contexts to praise someone's abilities or character.
He is a talent who is hard to replace with anyone else.
This project requires an expert who is irreplaceable.
かけがえのない is a more common and general adjective meaning 'irreplaceable' for things or people, while 余人をもって代えがたい is a formal, set phrase specifically about a person being irreplaceable.
Standard modern spelling with 代えがたい.
Variant using the kanji 難い for がたい; slightly more formal or literary.
Archaic spelling with 以て for もって; mainly encountered in older texts.
Mixed archaic-modern spelling; rarely used.
A set phrase composed of 余人 (another person), を以て (by means of, with), and 代え難い (hard to replace). The expression is literary and formal, emphasizing the unique value of an individual.