Misa Amane's stalker

Misa Amane's stalker is a man who is obsessed with Misa Amane.

Anime and Manga
Misa Amane is walking when suddenly a man she has never met before jumps out at her and professes his love. He mourns the fact that she will not be with him, and so he tells her that he will commit murder-suicide. This is to be the way Misa Amane will die, however, Gelus a Shinigami who has been watching Misa for some time and has fallen in love with her, had been watching to see how Misa would die. Seeing that he can prevent her death, Gelus kills Misa's stalker with his Death Note. Having broken an important Shinigami rule, Gelus dies as punishment, leaving his notebook behind.

Rem, a Shinigami who had been watching Misa with Gelus, curious as to how she would die, takes the Death Note and drops it into the human world for Misa to find, as she deems to be appropriate in light of the circumstances. Misa finds Gelus' notebook and eventually meets Rem.

Film
Misa has a stalker in the live action film Death Note: The Last Name, however, this one is much more fleshed out.

Known as Ryotaro Sakajo, he is the assistant director during the filming of Misa Amane's "Misa-Misa's Happy Sweets" video. He is obsessed with Misa, collecting a used tissue of hers after she throws it in the trash. In a sequence bridged between the two films, Sakajo corners Misa and brandishes a knife, stating that he wishes to die with her. Gelus, watching from the Shinigami realm, kills him to save Misa's life. In doing so, Gelus dies and his Death Note drops near Misa.

In the movie, Sakajo is first seen watching Misa film her cooking show, Misa-Misa's Happy Sweets. While off-set, Misa blows her nose, and throws the tissue into a small garbage can. After Misa has left, Sakajo takes the tissue out and places it into his pocket.

Sakajo presumably follows Misa outside after she leaves the TV station, eventually causing her to flee. Claiming that he wants to reunite Misa with her family, Sakashiro chases her with a knife and says that he wants "to die for her."