In the film, "Zelig" what famous writer first discovers Leonard Zelig's unique chameleon like abilities?

In Woody Allen’s 1983 faux-documentary comedy Zelig, F. Scott Fitzgerald appears near the beginning of the film, as one of the first people to take notice of Zelig’s mysterious personality (chameleon) alterations. Zelig is clearly observed at the party by F. Scott Fitzgerald, who notes that Zelig is able to relate to the affluent guests in a very sophisticated (refined) all inclusive way.

Overall, with Leonard Zelig, he represents a fantasy and a nightmare of American Jewish assimilation taken to its extremes. By disappearing into the dominant culture of his time, Zelig has found a way to get ahead and escape the ever present specter of Antisemitism. By using satire and fantasy, Zelig is able to present himself as a Jew so pathologically desperate to fit in that his conformity takes on physical and psychological components. For Zelig his radical assimilation yields financial and professional rewards. He becomes a fad, a craze, a Jazz Age sensation. But his actions also strip him of his identity, agency, and individual humanity.

Zelig’s actions in the 1983 film, resonate strongly and work as an unusually blunt allegory for some of the perils and rewards directly related to Jewish assimilation for people (those like Zelig) in America.