John Harker was the fiancé of Mina Seward and lived in London, England during the early 1930s.  Mina and he attended the symphony with her friend Lucy Western and Mina's father, Doctor Seward. It was at this time that John first met Transylvanian nobleman, Count Dracula. John was also present when Mina began to exhibit symptoms of vampirism. John and Mina stayed at her father's sanitarium and John kept close vigil over Mina. The learned scholar, Professor Van Helsing, warned John about Count Dracula, positively identifying him as a vampire. Dracula terrorized John and Mina on the terrace of her room at the sanitarium in the form of a bat. Shortly thereafter, John and Professor Van Helsing followed Dracula's lackey, Renfield, to Carfax Abbey where Van Helsing plunged a stake into Dracula's heart. John rushed to Mina's side to make certain that she was safe.
- In the novel, Jonathan Harker was a central character and most of the prose was taken from his point of view. The 1931 film however, greatly marginalized Harker's role in the story, and he existed as little more than a witness to the events taking place around him. One element that seems to be common to all versions of the character is his relationship to Mina and his presence at the climax of the story when Van Helsing and he (usually accompanied by others), fights against Dracula for the final time.
- The character of Jonathan Harker has appeared in nearly every film adaptation of Dracula. He has been played by actors such as David Manners, John Van Eyssen, Murray Brown, Bosco Hogan, Bruno Ganz, Keanu Reeves, Steven Weber, Hardy Krüger, Jr., Rafe Spall and Johnny A. Wright.
- Most other versions of the character are identified by his full name, Jonathan Harker. This is the only version to use the shortened form, John Harker.