Jealous, also known as Gelus, is a Shinigami, or god of death, who appears in a flashback within the story of Death Note. His role is brief but pivotal, serving as a key example of the rules governing the Shinigami realm and providing the catalyst for another character's entry into the human world. His physical form is distinctive and deliberately unappealing, appearing small and doll-like, as if poorly sewn together from mismatched patches of fabric. Despite having two empty eye sockets, he possesses only a single eye, which adds to his strange and somewhat pitiful appearance. The artist intentionally designed him to look pathetic and stupid rather than beautiful, believing this would allow readers to relate to him and sympathize with his unfortunate circumstances.

In terms of personality, Jealous stands in stark contrast to the majority of his fellow Shinigami, who are portrayed as apathetic and bored with their endless existence. Unlike them, Jealous possesses a rare capacity for deep caring and affection toward humans. He is described as kind, quiet, gentle, and possessing a pure heart. Instead of idly passing the time by writing names to extend his own lifespan, Jealous became captivated by a young human woman named Misa Amane. He spent an extended period watching over her from the Shinigami Realm, developing a powerful and genuine affection for her that bordered on love.

This love is the core of his motivation. Jealous was driven not by a desire to cause death but by a compelling need to protect. When he observed that it was Misa's predetermined final day, he watched intensely, wanting to see how she would meet her end. Upon witnessing a deranged man preparing to stab her to death, Jealous could not bear the thought of losing her. Acting on his feelings, he directly intervened by writing the name of Misa's destined murderer in his own Death Note, killing the man and saving Misa's life. This selfless act of love directly violated a fundamental rule of the Shinigami, as they are forbidden from extending a human's lifespan. As punishment for his transgression, Jealous crumbled into a pile of rust and sand and died, leaving behind only his Death Note.

Jealous's role in the larger narrative is primarily as a figure in a flashback, related by the Shinigami Rem to Misa Amane. His actions have several significant consequences. His death provides a clear illustration of the paradox that a Shinigami can only die by falling in love with a human and choosing to save them. Furthermore, it is through his sacrifice that the Death Note originally belonging to Jealous comes into Misa's possession. Following his death, Rem, who witnessed the event, delivers his notebook to Misa in the human world, believing this was his final wish. This act directly enables Misa to later make a second deal for the Shinigami Eyes, as she now possesses her own Death Note.

The character does not undergo development because he exists only within a single, fatal event. His entire known story is one of quiet observation leading to a single, decisive moment of sacrifice. His development is less about change and more about the revelation of his unique capacity for love, which ultimately proves to be his undoing. Regarding notable abilities, Jealous possesses the standard powers of a Shinigami. He is able to see the names and remaining lifespans of humans, a power that allowed him to understand Misa's fate. He can kill any human whose name he writes in his Death Note while picturing their face, a power he used to kill the stalker. A unique and somewhat ironic detail is that the artist imagined Jealous having difficulty writing names in the Death Note, a trait that adds to his characterization as a clumsy and pitiable being for whom this final act was likely a struggle.