expression
(not) a single person; (no) one
Used with a negative verb to emphasize that absolutely no one does or is something. Stronger than simply saying 誰も.
See also: として
誰一人として彼の話を信じなかった。
Not a single person believed his story.
その会議には誰一人として遅刻しなかった。
No one was late for that meeting.
誰も is the standard 'no one' with a negative verb, while 誰一人として adds stronger emphasis that there is absolutely not even one person.
Combination of 誰 (who) + 一人 (one person) + として (as, even), literally 'even as one person'. The phrase emphasizes the absence of any individual.