Every celebrity photographer in a pack outside a nightclub is named after one fictional man. He was a minor character in an Italian film.
The film was La Dolce Vita, directed by Federico Fellini and released in 1960. It follows a gossip journalist through a summer of Roman parties. At his side is a news photographer called Paparazzo, played by Walter Santesso. He chases stars and shoots whatever he can get.
English took the name almost at once. Etymonline dates the word in English to 1961. By the late 1960s, according to Wikipedia, it was a general term for intrusive photographers. English usually uses the Italian plural, paparazzi. The singular, paparazzo, still turns up for a single photographer.
Where Fellini got the name is less settled. There are at least three stories, and they do not agree.
Fellini's own account was about sound. He said the name suggested "a buzzing insect, hovering, darting, stinging." Some retellings go further and claim it was Italian slang for a mosquito. That detail is harder to pin down than Fellini's quote.
The second story comes from Ennio Flaiano, who co-wrote the script. He said that he or Fellini opened a book at random and found the name there. The book was By the Ionian Sea, a 1901 travel narrative by the English writer George Gissing. In it, Gissing mentions a hotel keeper in Calabria called Coriolano Paparazzo. Etymonline notes that the surname is said to be common in Calabria.
The third story is about dialect. In the Abruzzo dialect that Flaiano spoke, a paparazzo is a kind of local clam. Wikipedia reports that the word was also used as a metaphor for the shutter of a camera lens.
These accounts are not all exclusive. A name found in a travel book could also have sounded right for a darting pest. What is certain is the path from screen to street. A surname with no special meaning in the film became the label for a whole trade.