unqualified person; incompetent person; square peg in a round hole
Formal term for someone who is not suited or lacks the necessary qualifications for a position or task. Often used in professional or evaluative contexts.
He was judged to be unqualified for that job.
You shouldn't put an incompetent person in an important post.
不適格 is a noun or na-adjective meaning 'disqualification' or 'ineligibility', often used in rules or criteria, while 不適任者 specifically refers to a person who is unfit for a role.
無能 means 'incompetence' or 'inability' and is a more general and harsher term, not limited to a specific position.
Compound of 不 (not), 適任 (suitable for a post), and 者 (person). The word is a straightforward Sino-Japanese formation.