The word paparazzi comes from Paparazzo, the surname of a photographer character in Federico Fellini’s 1960 film La Dolce Vita. After the movie became famous, the name started being used more broadly for photographers who aggressively follow well known people and try to capture candid pictures.
In Italian, Paparazzo is singular and paparazzi is plural. English borrowed the plural form and made it the common general term. That is why people usually say paparazzi were waiting outside the hotel, not paparazzo were waiting.
The meaning also narrowed in a specific way. It does not usually mean all photographers. It usually refers to photographers who pursue celebrities in public, often hoping for unplanned or revealing images.
- General photographer: a wedding photographer took portraits.
- Paparazzi: paparazzi followed the singer to get candid photos.
So the modern word is a good example of a fictional name turning into a widely used real world label.