Zechs Merquise, born Milliardo Peacecraft, was the prince and male heir of the pacifist Sanc Kingdom. After the United Earth Sphere Alliance destroyed his kingdom in AC 182, killing his parents, he assumed the alias Zechs Merquise (derived from the German "Sechs," meaning six) and concealed his identity behind a silver mask. He infiltrated the Earth Alliance, and later its elite OZ special forces, seeking vengeance against those responsible for his family's downfall. Rising to the rank of Colonel within OZ, he earned the moniker "Lightning Count" or "Lightning Baron" due to his extraordinary combat speed and piloting skill. This reputation stemmed notably from a counter-terrorism operation in AC 191 where he neutralized a threat within minutes, prompting his friend and commander Treize Khushrenada to remark that he "fights like lightning." He piloted the notoriously unstable OZ-00MS Tallgeese prototype, mastering it despite its lethal reputation. He later commandeered the XXXG-00W0 Wing Gundam Zero after sacrificing the Tallgeese. Following a stalemate battle with Heero Yuy, he traded the Wing Zero for the OZ-13MS Gundam Epyon. His piloting skills matched the Gundam pilots, marked by exceptional reflexes and physical endurance. He demonstrated the ability to adapt to advanced systems like the ZERO System, though he initially struggled with its mental strain. Profoundly conflicted, Zechs was torn between his pacifist heritage and his identity as a soldier. Believing his actions rendered him unworthy of his family name and unfit to restore the Sanc Kingdom, he designated his sister Relena Peacecraft as its rightful heir. This self-loathing manifested intensely when Treize addressed him as "Milliardo Peacecraft." He often displayed chivalry, sparing enemies in Relena's presence or allowing opponents to recover, yet executed missions with ruthless efficiency. His core motivation evolved from personal vengeance towards forcing lasting peace through overwhelming conflict, believing humanity required a singular threat to unite against. Key events in his arc included an early duel with Heero Yuy during Operation Meteor, secretly rebuilding the Wing Gundam after Heero self-detonated it, and confronting OZ leadership when his identity was exposed during Operation Daybreak, where he executed the Alliance commander responsible for the Sanc Kingdom's destruction. After his public unmasking fractured his ties with OZ, he fled to space, briefly serving as a Sanc Kingdom ambassador under his real name. Disillusioned by colonial leaders embracing militarism, he resumed his Zechs persona and destroyed OZ's mobile doll forces. Following Relena's dissolution of the Sanc Kingdom, he descended into despair and accepted leadership of the colonial extremist group White Fang. As their commander, he declared war on Earth using the battleship Libra to impose peace through fear. His final battle against Heero during the Eve Wars ended in defeat, and he sacrificed himself to destroy Libra's falling segment, seemingly perishing in the explosion. He resurfaced a year later in AC 196 during the Mariemaia Army uprising, joining the peacekeeping organization Preventers under the codename "Wind." Piloting the OZ-00MS2B Tallgeese III, he aided in thwarting a colony drop on Earth. After this conflict, he reconciled his dual identities and abandoned his quest for vengeance. He married his longtime comrade Lucrezia Noin, and the couple had twins named Naina and Mille Peacecraft. They relocated to Mars to lead terraforming efforts.