Family-Treize Khushrenada (cousin) and Duke Dermail (grandfather)
Dorothy Catalonia is considered the antithesis of Relena Peacecraft; whereas Relena advocates total pacifism without fighting, Dorothy strongly believes in human confrontation and conflicts in order to achieve such a goal. She also believes that human conflict will always be a part of life. Dorothy attended the school in the Sanc Kingdom, where Relena Peacecraft was teaching women total pacifism, in the name of her biological and adoptive father. However, she was really a spy for the Romefeller Foundation as her grandfather was Duke Dermail. Though Relena's aide-de-camp expressed doubts about Dorothy, but Relena was confident that she would accept her ideals in time.
Though not much is known about Dorothy, from the anime series it is seen that she is a great orator, able to convey her ideas and thoughts to others. Being a spy for the Romefeller Foundation, she knows a few things about being an observer. Dorothy soon headed out into space, to join White Fang leader Zechs Merquise, going by his real name Milliardo Peacecraft. At first, Milliardo's first thought was to destroy her shuttle, as she was from Romefeller, but relents when she passionately details his history. She becomes his second in command, witness to him using Libra's main cannon to attack Earth. When Zechs gives Dorothy the ZERO System to control the Virgo II mobile dolls, her skills as a tactician increase significantly, able to fend off the Gundam Pilots. However, in reality, Dorothy is putting up her facade of a strong woman, while she's actually insecure, lonely and traumatized by the horrors of war, and she'd stop at nothing to put an end to the carnage.
During the battle between White Fang and OZ; the Gundams, though not allied with Treize, were determined to stop White Fang from completing Operation Meteor. Dorothy came face-to-face with Quatre, challenging him to a fencing duel. As they fight, though Dorothy claims to love warfare, she deeply hates it for taking her father's life, and puts on a strong face to the world. She then is able to wound Quatre. However, Trowa intervenes. Dorothy then leaves Libra, as it falls to Earth but it is destroyed by Wing Zero.After the Earth Sphere Unified Nation is formed, Dorothy and Lucrezia Noin pay their respects to Milliardo's grave, who had seemingly sacrificed himself to destroy Libra. However, the latter believes that he had survived.
Dorothy makes a cameo appearance in the Preventer 5 storyline featured in the Episode Zero manga. The manga also reveals in Relena's story that her father General Catalonia was the original leader of OZ who preceded Treize Khushrenada and was killed around the time of A.C. 193 which in the timeline as shown in the manga is when Trieze took control of OZ.
When Relena calls out to the people stand up against the Mariemaia Army, Dorothy appeared before the crowd watching the big TV screen. She taunted them as dogs wagging their tails and go to their master. The people then realize that peace doesn't come easy for them and that they have to earn it. Dorothy decided to help them in their moment of courage by providing trucks for transportation to Brussels, the Earth Sphere Unified Nation capital, where the Preventers and Gundams were fighting the Mariemaia Army. There, the people, in a pacifist way, stood up against those who think to conquer them. Eventually, it led to complete peace in the Earth Sphere.
In M.C. 0022, Dorothy T. Catalonia is the President of the Earth Sphere Unified Nation. She personally gives Preventer agent Kathy Po the orders and data necessary to enact Operation Mythos. When Kathy views Treize Khushrenada's personal history in order to take part in the Operation, she observes a 5 year old Dorothy with her father, OZ leader General Chilias Catalonia. She notes Dorothy is a charmer and speaks similarly even then to how she does in the series, exhibiting an already high level of intelligence. She seems to have been enamored with Treize as a child, wanting to "marry" him.