'documentarian' originates from English, specifically from the noun 'documentary' plus the agentive suffix '-an' (or '-arian'), where 'document' ultimately derives from Latin 'documentum' meaning 'a lesson, proof' (from 'docēre' meaning 'to teach').

'documentarian' developed in English in the early 20th century as a formation from 'documentary' (itself from Medieval Latin/Old French through Latin 'documentum') with the suffix '-an'/'-arian' to indicate a person associated with or practicing something.

Initially, roots related to 'document' referred to a 'lesson' or 'proof'; over time the term 'documentary' came to mean a non-fiction film or program presenting factual material, and 'documentarian' came to mean 'a maker or practitioner of documentaries.'