Dorothy Catalonia is the granddaughter of Duke Dermail, the influential leader of the Romefeller Foundation, and a distant cousin of the charismatic officer Treize Khushrenada. Her father was General Catalonia, the original leader of the organization OZ before Treize. At fifteen years old, with platinum blonde hair and purple eyes, Dorothy initially presents herself as an ordinary student at a school run by Relena Peacecraft in the Sanc Kingdom, but this is a cover for her true mission as a spy for the Romefeller Foundation.

Dorothy is designed as a philosophical opposite to Relena Peacecraft. While Relena advocates for total pacifism and the elimination of war, Dorothy publicly argues that conflict is an essential and ineradicable part of human nature. She possesses a quick, eloquent, and commanding manner of speech, able to sway the elderly politicians of the Romefeller Foundation with her sharp arguments. However, this admiration for warfare is later revealed to be a complex facade. Deep within, Dorothy despises war, which she blames for taking her father's life. Her true, hidden motivation is the belief that humans will only fully renounce war after experiencing a conflict so devastating and tragic that they become permanently traumatized by its horrors. This contradiction defines her character; the strong, war-loving persona she projects is a mask worn to hide deep-seated insecurity, loneliness, and trauma.

In the story, Dorothy plays a pivotal role as an agent of chaos and a catalyst for change. After revealing her true allegiance during an attack on the Sanc Kingdom, she offers Relena a choice: become a symbolic figurehead for Romefeller to stop the bloodshed. Following Relena's rise and fall as Queen of the World, Dorothy's ambitions lead her to space. She manages to join the rebel organization White Fang by demonstrating an intimate and passionate knowledge of its leader, Zechs Merquise, also known as Milliardo Peacecraft, and becomes his sub-commander.

Her key relationships are complex and often antagonistic. She shares a tense, competitive dynamic with Relena, whom she both observes and challenges. She develops a significant rivalry with the Gundam pilot Quatre Raberba Winner, which culminates in a dramatic fencing duel. Dorothy's family ties are also notable; her grandfather, Duke Dermail, is a figure she skillfully manipulates and ultimately sends to his death in space. Her respect for Treize Khushrenada, her cousin, shapes some of her political maneuvers, and her admiration for Zechs leads her to serve as his second-in-command.

Throughout the series, Dorothy’s development shows a shift from a purely manipulative antagonist to a more ambiguous figure. During the final battle, she confronts Quatre and admits the truth about her hatred for war, revealing her vulnerability. After the war, she makes a surprising appearance during the Mariemaia rebellion, not as a combatant, but as an instigator. She taunts a passive crowd of civilians into action, helping them find the courage to stand up for peace themselves, showing a different application of her forceful personality.

Dorothy possesses several notable abilities. She is a highly skilled fencer, capable of holding her own in combat against trained Gundam pilots like Heero Yuy and Quatre Raberba Winner. More remarkably, she has a powerful mental fortitude that allows her to use the Zero System, a sophisticated battle-computer interface that drives most individuals insane. She uses this system to command squadrons of mobile dolls with exceptional tactical skill. Later in the timeline, in the serial novel Frozen Teardrop, Dorothy is depicted as having become the President of the Earth Sphere Unified Nation, where she continues to exert her influence on the political stage.