Ali al-Saachez is a primary antagonist known as a former Middle Eastern guerrilla who developed an intense love for conflict and eventually became a freelance mercenary. His past is rooted in the leadership of the KPSA, a terrorist organization he created in the Middle East approximately a decade before the main events of the story. During this time, he was responsible for heinous acts, including ordering children to commit murder as a proof of faith and orchestrating a bombing in Ireland that killed the family of Neil and Lyle Dylandy. His most significant act from this period was the kidnapping and indoctrination of a young boy named Soran Ibrahim, whom he trained as a child soldier and who would later become the Gundam Meister known as Setsuna F. Seiei.

Saachez possesses a deeply nihilistic and sociopathic personality. He is a self-professed enthusiast of war, violence, and chaos, engaging in battle purely for the joy and thrill it provides. He is described as underhanded, ruthless, and selfish, taking pleasure in the suffering of others to the extent that other characters refer to him as a monster. He is content with the mercenary life not for any ideological reason but because it allows him to kill and profit from it. He is also intellectually dangerous, skilled in deception and manipulation. A notable personal quirk is his preference for the color crimson, which he uses to adorn his clothing and mobile suits.

Throughout the first season, Saachez operates under various aliases, including Gary Biaggi within the AEU French Foreign Legion, to continue his work. His primary motivation is to perpetuate conflict, and he actively works to destabilize regions like Azadistan to incite war. He is hired by PMC Trust to capture a Gundam and later by the schemer Alejandro Corner. In this role, he eliminates the Trinity siblings, killing Michael and Johann and stealing the GNW-002 Gundam Throne Zwei. He also murders the journalist Kinue Crossroad after revealing his true nature to her. In the second season, he becomes an agent for the Innovators, a group of artificial beings, and pilots the advanced GNW-20000 Arche Gundam, continuing his campaign of terror, including the destruction of Azadistan.

His most significant relationships are defined by the trauma he inflicted. He is the primary nemesis of Setsuna F. Seiei, who seeks to overcome the past Saachez represents. He is also the sworn enemy of Lockon Stratos, specifically Neil Dylandy in the first season and his twin brother Lyle in the second, both of whom seek to avenge their family. His development is not one of redemption but of a consistent and escalating pursuit of his savage desires. After surviving the destruction of the Throne Zwei in a battle that killed Neil Dylandy, he reappears with the Arche Gundam, his skills and ruthlessness undiminished.

In terms of abilities, Saachez is one of the most formidable pilots in the series. He is highly competent in all forms of combat but is most lethal in close-quarters situations, both inside and outside a mobile suit. His combat style is reflected in his choice of units, which are exclusively designed for close-range engagement. His skills are rooted in his time leading the KPSA, where he brainwashed and trained children in combat techniques, making him a deadly mentor to his eventual adversaries. His end comes when he is cornered by Lyle Dylandy. After his mobile suit is disabled by a system control hack, he attempts to flee but is confronted. When he tries to take advantage of his opponent's hesitation, he is shot and killed by Lyle, finally bringing his reign of violence to an end.