Gelsandra, also known as Gel Sadra, is the primary antagonist in the series Gatchaman II, serving as the commander of the terrorist organization Galactor after the departure of their predecessor, Berg Katse. Their background is rooted in profound tragedy; they were originally a very young child named Sammie Pandora, approximately three to four years old, and the child of scientists Dr. Sylvie Pandora and Domenico Pandora. After surviving a meteor attack orchestrated by the entity Leader X that sank the cruise ship they were on, Sammie was abducted by X. Leader X then subjected the child to accelerated aging and genetic modification, artificially maturing them into a twenty-five-year-old adult and brainwashing them to become a loyal, ruthless servant.

As a result of this forced mutation, Gelsandra possesses a highly ambiguous physical presentation. They have blond hair and brown eyes, but their form is often described as androgynous or intersex, with a body that appears feminine combined with a flamboyant, falsetto voice that sounds masculine, reminiscent of kabuki theater style. Their body remains largely covered for most of the series by a distinctive, clownish uniform that includes a purple tunic, a large blue collar, and a headdress that obscures their eyes. Personality-wise, Gelsandra is manipulative and skilled, capable of abducting scientists and rebuilding Galactor's forces within a month. However, due to being artificially aged from a young child, they are emotionally immature, prone to childish tantrums when facing defeat, and can behave more comically than their predecessor. They intensely hate Berg Katse, insisting they are different from that fool, and once destroyed a portrait of Katse while deriding the room they decorated as having bad taste. Gelsandra has several verbal tics and catchphrases, including Failure is the mother of success, Albatross flying into the fire, and the curse Onore, onore, Gatchaman!.

In the story, Gelsandra's primary role is as the field commander of Galactor, leading operations against the Science Ninja Team to further Leader X's plans for world domination and the Solar Shift plan. Despite their loyalty to X, Gelsandra harbors hidden memories of their past life. This culminates in the final episodes when they remember their mother, Dr. Sylvie Pandora, and abduct her for a reunion. Although Dr. Pandora feels a psychic familiarity, she is horrified and cannot initially accept the mutated creature before her as her child. Leader X seals this tragedy by trapping Dr. Pandora in a rocket and launching her into space to explode, killing her. Witnessing her death causes a complete emotional change of heart in Gelsandra, turning them against Leader X. They betray Galactor and assist the Science Ninja Team, specifically Ken, in finding X's main computer core to defeat him.

Gelsandra's development is the central tragedy of the series arc. They transform from a brainwashed and cruel villain into a repentant figure. After being mortally wounded during the final assault on X's base, a dying Gelsandra walks alone to a hill covered in flowers. Moved by the beauty of the Earth, they express deep regret for trying to destroy it and wish to be reborn. Overcome by their injuries, they pass away while seeing a vision of their mother telling them it is time to rest. As they die, their body reverts to the small child form of Sammie and disperses into light, with their spirit following their mother and only their empty clothes remaining. Notable abilities include a fast and comical escape technique that they inherited from Katse, as well as strategic and leadership skills sufficient to command a global terrorist organization for Leader X.