noun
Refers to the person who first started an organization, movement, field, or system. Often used in formal or historical contexts.
彼はこの会社の創始者です。
He is the founder of this company.
その理論の創始者は誰ですか。
Who is the originator of that theory?
設立者 is used for the person who established an organization or institution, often with a legal or formal nuance.
Compound of 創始 (sōshi, 'founding, origination') + 者 (sha, 'person'). The word 創始 itself is a Sino-Japanese compound of 創 (sō, 'create, originate') and 始 (shi, 'begin').