Haggar serves as a powerful witch and key antagonist aligned with King Zarkon. Her primary role involves creating destructive robeasts to combat Voltron, utilizing dark magic and hypnosis to further Zarkon's conquests. Her background reveals she was not always evil; she was once a virtuous and beautiful sorceress who used her powers for good. Zarkon seduced her with false promises and lies, leading to her corruption and transformation into an envious, malevolent figure fixated on power. Despite moments of self-awareness about her misery and past goodness, she consciously rejects redemption, prioritizing the retention of her dark abilities over returning to her former self.

In "Fleet of Doom," Haggar's insecurity intensifies when Zarkon deems her magic ineffective and replaces her with a Drule scientist. Determined to prove her worth, she acquires new dark powers and captures Princess Allura's soul, trapping her in an extradimensional nightmare realm. There, Haggar admits her past virtue and beauty but blames Zarkon for her downfall. Allura attempts to appeal to Haggar's lingering goodness, offering to help "let the good Haggar out," but Haggar violently rebuffs these efforts, refusing to relinquish her power. When Keith confronts her in the dimension, she challenges him to identify the real Allura among decoys. After failing to defeat Keith, Haggar prepares to kill him, but Allura intercedes, pleading once more for Haggar to embrace her good side. This confrontation causes Haggar's suppressed goodness to manifest as a separate, benevolent entity. Though momentarily overwhelmed, Haggar resists reintegration, fearing the loss of her powers. As the dimension collapses, Allura offers escape, but Haggar refuses, declaring it "too late" for her and forcibly returning Allura and Keith to their world. She subsequently reabsorbs her good side and returns to serving Zarkon.

Outside "Fleet of Doom," Haggar's character shows variations. In "Defender of the Universe," she appears as Zarkon's loyal sorceress, credited in the American adaptation with originally splitting Voltron into five components. Her past as a once-good figure is noted as a departure from her Japanese counterpart. She maintains adversarial relationships with Galra commanders like Yurak, who distrusts her magic. "Voltron: The Third Dimension" depicts her initially in hiding after Zarkon's defeat, later allying with Prince Lotor under a power-sharing agreement where she would gain the magic of the lions upon his conquest.

"Voltron: Legendary Defender" reimagines Haggar as Honerva, an Altean alchemist who discovered quintessence with King Alfor and Emperor Zarkon. Her obsession with the energy source led to her corruption and memory loss after exposure to interdimensional rifts. Reborn as Haggar, she serves the Galra Empire for millennia, creating robeasts and weaponizing quintessence. After regaining her memories and facing the consequences of her actions—including the loss of her son Lotor—she reverts to Honerva. Consumed by grief, she attempts to destroy all realities before being stopped by Voltron. Purified of dark magic by Allura, she sacrifices herself to undo her destruction, achieving a redemption unattained in other continuities.

Throughout all iterations, Haggar possesses a blue cat named Cova (or Kova in "Legendary Defender"), which acts as her familiar and occasionally assists in her spells.