Answer by taking a quote from the following article:

Zelig is a 1983 American mockumentary film written and directed by Woody Allen and starring Allen and Mia Farrow. Allen plays Leonard Zelig, a nondescript enigma, who, out of his desire to fit in and be liked, takes on the characteristics of strong personalities around him. The film, presented as a documentary, recounts his intense period of celebrity in the 1920s and includes analyses from contemporary intellectuals. Zelig was photographed and narrated in the style of 1920s black-and-white newsreels, which are interwoven with archival footage from the era and re-enactments of real historical events.

Zelig has an overall approval rating of 100% on the review aggregator Rotten Tomatoes based on reviews from 24 professional critics with an average score of 7.9/10. In his review in the New York Times, Vincent Canby observed:  [Allen's] new, remarkably self-assured comedy is to his career what ... Berlin Alexanderplatz is to Rainer Werner Fassbinder's and ... Fanny and Alexander is to Ingmar Bergman's ... Zelig is not only pricelessly funny, it's also, on occasion, very moving. It works simultaneously as social history, as a love story, as an examination of several different kinds of film narrative, as satire and as parody ... [It] is a nearly perfect - and perfectly original - Woody Allen comedy.  Variety said the film was "consistently funny, though more academic than boulevardier", and the Christian Science Monitor called it "amazingly funny and poignant". Time Out described it as "a strong contender for Allen's most fascinating film", while TV Guide said, "Allen's ongoing struggles with psychoanalysis and his Jewish identity - stridently literal preoccupations in most of his work - are for once rendered allegorically. The result is deeply satisfying".  In Empire magazine's poll of the 500 greatest movies ever made, Zelig was ranked number 408. Chris Nashawaty of Entertainment Weekly listed the work as one of Allen's finest, lauding it as "a spot-on homage to vintage newsreels and a seamless exercise in technique." The Daily Telegraph film critics Robbie Collin and Tim Robey also named it as a career highlight and argued, "The special effects, in which Allen is seamlessly inserted into vintage newsreels, are still astonishing, and draw out the aching tragicomedy of Zelig's plight. He's the original man who wasn't there." Calum Marsh of Slant magazine wrote, "We are infinitely pliable. That's the thesis of Zelig, Allen's wisest film, which has much to say about the way a person can be bent and contorted in the name of acceptance. Its ostensibly wacky conceit [...] is grounded in an emotional and psychological reality all too familiar to shrug of [sic] as farce. We'll go very far out of our way to avoid conflict. Zelig seizes on that weakness and forces us to recognize it."

Is it the first one to receive 100%?