One of my first posts on Sino-Korean and using Hanja to learn Korea was on 人 Hanja, which is where 인 in 인간 and many other words come from. While 人 is related to people, the Hanja we are covering today is also related, but more about describing a person. 者 or 자 relates more to describing people with a specific job, characteristic, status, etc.. The breakdown of the Hanja from many of these comes out to “the one who __”.
Professions
가입자: member/policyholder
강연자: lecturer
교육자: educator
기자: journalist
기술자: technician/engineer
사자: messenger/envoy
사회자: chairperson or host/MC (lit. take charge, assemble, those who)
연기자: performer (not usually used when talking about actors; has a wider range)
지휘자: conductor
철학자: philosopher