Hagar is a powerful witch and a central antagonist in Voltron: Defender of the Universe, serving as the most loyal and trusted confidant to the evil King Zarkon. Her primary function within the ruling hierarchy of Planet Doom is to use her extensive dark magical abilities to further the empire's conquest of the galaxy. She is most notorious for being the creator of the monstrous Robeasts, or Galran Beast Fighters, which are sent to battle Voltron as the primary threat of each episode. Her expertise in dark magic makes her an invaluable asset to Zarkon, and she is often seen casting spells, creating potions, and performing rituals to achieve her master's goals.

The background of Hagar reveals a tragic fall from grace. In the continuity of Defender of the Universe, it is established that she was not always the malevolent, haggard witch known to the heroes of Arus. She was once a good and beautiful sorceress who used her powers for virtuous purposes. Her transformation into an evil and ugly figure was a direct result of Zarkon's influence, as he seduced her with false promises and lies, leading to her corruption. Her personality reflects this bitter history; she is envious, malevolent, and fiercely fixated on retaining her dark power, often showing moments of self-awareness about her misery and lost goodness, yet actively rejecting any chance at redemption for fear of losing her abilities.

In her role within the story, Hagar is not merely a support character but a driving force behind many of the Voltron Force's greatest challenges. Beyond creating the Robeasts, she is credited in the American version of the series with being directly responsible for originally splitting Voltron into its five lion components, a feat she accomplished by disguising herself as a goddess in distress to place a curse on the mighty robot. She is also known for using her magic to cast hypnotic spells over people. Her relationship with King Zarkon is complex; while she is utterly loyal to him, their dynamic is rooted in his manipulation of her. It is implied in the film Fleet of Doom that she was once one of Zarkon's love interests or a concubine, but her insecurity becomes apparent when Zarkon deems her magic ineffective and attempts to replace her, driving her to desperate acts to prove her worth. She also holds an adversarial relationship with other Galra commanders, such as Yurak, who distrust her sorcery.

Hagar's development is largely static throughout the main series, defined by her unyielding commitment to evil. However, a significant exploration of her character occurs in the crossover film Fleet of Doom. In this story, after being cast aside by Zarkon, she acquires new dark powers and captures the soul of Princess Allura. When confronted by Allura and the Paladins within an extradimensional nightmare realm, Hagar's suppressed goodness manifests as a separate entity. Although she is momentarily overwhelmed by this vision of her former virtuous self, she violently refuses Allura's offer of help and rejects reintegration, choosing instead to remain a powerful witch. She proclaims it is too late for her, forcibly returns her captives to their world, and reabsorbs her good half, solidifying her return to Zarkon's service.

Regarding her notable abilities, Hagar is a master of dark magic and sorcery. This includes the creation of Robeasts, casting powerful offensive spells, hypnotism, and interdimensional manipulation as seen in Fleet of Doom. She often employs a blue cat named Cova, who acts as her familiar and frequently assists her in casting spells and performing rituals. Her magical prowess is such that she is considered one of the greatest threats to the universe, second only to Zarkon himself.