What is the name of the protagonist in 'The King of Comedy'?

The protagonist of 'The King of Comedy' is Rupert Pupkin.

Played by Robert De Niro, Rupert is a struggling stand-up comedian who is convinced that he is destined for television stardom. He becomes fixated on Jerry Langford, a successful late-night host played by Jerry Lewis, and interprets their brief encounter as the beginning of a professional friendship. Rupert's elaborate fantasies blur the line between ambition and reality.

When Langford repeatedly rejects him, Rupert escalates from unwanted persistence to kidnapping, enlisting another obsessive fan named Masha. The story satirizes celebrity culture, television fame and the belief that notoriety is more important than talent. Rupert even calls himself “the King of Comedy,” despite having little evidence that audiences share his assessment.

Scorsese's 1982 film is often discussed as a dark companion to 'Taxi Driver', since both feature De Niro as an isolated man living inside a distorted personal mythology. Rupert Pupkin is not Travis Bickle, Henry Hill or Jordan Belfort; those are protagonists from other films.