Early 17th century (in the sense 'personify'): from in-² 'into' + Latin persona 'person', on the pattern of incorporate.

• person from Middle English:

  When first used in English person meant ‘a role or character assumed in real life or in a play’ as well as ‘an individual human being’. The first sense has largely been taken over by persona, which came directly in the mid 18th century from the source of person, Latin persona ‘actor's mask, character in a play’, and also ‘human being’. The Latin term was also used by Christian writers as a term for the rector of a parish, what we would now call a parson (Middle English). From the same source come impersonate (early 17th century) originally meaning ‘personify’, and personnel (early 19th century) from French and which still keeps the original stress on the final syllable normal in that language.