Xeno Houston Wingfield is a central figure in the story, introduced as a formidable antagonist whose scientific genius rivals that of the protagonist. Before the world was petrified, Xeno was a scientist working for NASA. During this time, he received an unsolicited email from a young boy named Senku Ishigami. While his colleagues dismissed the message, Xeno was intrigued and responded, beginning a long-distance mentorship where he taught Senku various scientific principles. This correspondence continued for years, with Xeno only later discovering that the boy he had been teaching was the son of his colleague, Byakuya Ishigami. He eventually met Senku in person when the boy visited NASA.

Xeno possesses a personality that is both charismatic and deeply authoritarian. He is intensely rational and logical, viewing science as the ultimate form of power. Unlike Senku, who seeks the advancement of all humanity, Xeno is driven by a belief that the scientifically superior are meant to rule over the less sophisticated. Prior to the petrification, he famously stated that if civilization were to collapse, he would establish himself as a dictator. This ambition defines his actions in the new stone world. He is also shown to have a degree of theatricality and enjoys cleverness, stating his fondness for people who are either "honest to a fault" or "the world's greatest liars". Despite his ruthless pragmatism, he harbors a genuine, if complex, respect for his former protégé, Senku, and finds great satisfaction in engaging in high-level scientific discourse.

Xeno's primary motivation is to use his mastery of science to conquer the newly reset world. Upon freeing himself from the petrification, he immediately set about constructing a fortified base of operations in San Francisco. He established a factory capable of mass-producing munitions and weaponry, intending to expand his territory and subjugate others under his rule. His goal is not merely survival but the complete reordering of human society under his sole leadership. However, his immense curiosity about the origin of the petrification phenomenon, specifically the entity known as "Why-man," eventually becomes an equal or greater driving force, compelling him to collaborate with those he once sought to destroy.

Xeno serves as the main antagonist of the New America City Arc, where his advanced technology and military tactics pose the most significant challenge the Kingdom of Science has ever faced. His primary role is as a dark mirror to Senku, representing what the protagonist could become if he prioritized power over collective progress. After a series of conflicts and his eventual capture, Xeno transitions into a reluctant but crucial ally. His expertise, particularly as a former NASA scientist, becomes invaluable for the ultimate goal of building a rocket to reach the moon and solve the final mystery of the petrification. In this later phase, he acts as a key collaborator and strategic partner.

Xeno's most significant relationship is with Senku Ishigami, his former student turned rival. Xeno views Senku as both a threat and the only other individual capable of matching his intellect, leading to a dynamic of intense competition and mutual admiration. Equally important is his bond with Stanley Snyder, a master sniper and military tactician. They have been close friends since childhood, a partnership that originally involved illegal experiments to fund Xeno's research. In the stone world, Stanley is Xeno's most trusted enforcer and protector, fiercely loyal and personally committed to Xeno's vision. Their relationship is one of deep familiarity and mutual reliance, with Stanley often described as being overly helpful or even "wifelike" towards him. Xeno also commands a group of other skilled individuals, including a mechanic named Brody Dudley and the infiltrator Luna Wright, though his bond with Stanley remains paramount.

Xeno undergoes a notable development throughout the narrative. He begins as an unwavering antagonist who orders Senku’s assassination to eliminate a rival. However, after being captured, his priorities shift. Forced to cooperate with the Kingdom of Science, his scientific curiosity gradually overrides his tyrannical ambitions. He becomes deeply involved in investigating the petrification beam, leading him to willingly contribute his vast knowledge to the common goal of confronting Why-man. While his dictatorial leanings do not vanish entirely, he evolves from a world conqueror into a grudging ally whose need for scientific discovery tempers his desire for absolute control.

Xeno is an extraordinarily gifted scientist, likely the most technically advanced in the story due to his real-world experience at NASA. He demonstrates the ability to recreate modern weaponry, construct functioning aircraft, build a chemical factory, and develop a polygraph test from memory using stone-age resources. His expertise in physics and engineering allows him to quickly deduce the scientific principles behind his enemies' attacks. Senku himself acknowledges that Xeno’s technological base is superior to his own for a significant portion of their conflict. Beyond his intellectual abilities, Xeno is marked by a distinctive physical appearance, including grey, neck-length hair, a facial marking likely covering his petrification scars, and a usual attire consisting of a dark cloak and gloves.