Jean Havoc is a fictional character from the Fullmetal Alchemist franchise, serving as a loyal and skilled officer in the Amestris State Military. He holds the rank of Second Lieutenant and is one of the most trusted subordinates of Colonel Roy Mustang at the Eastern Headquarters. Havoc is a self-described country boy who grew up in a small town in eastern Amestris, where his family runs a general store. His decision to join the military was driven by a desire to protect his hometown with his own hands, a motivation rooted in growing up during a time of civil war. While he excelled in practical combat training at the military academy, he struggled with written exams and only graduated with significant help from his classmate and friend, Heymans Breda.

In terms of personality, Havoc presents a laid-back and often lazy demeanor, rarely seen without a cigarette in his mouth. This casual and sometimes sardonic exterior, however, masks a nature that is honest, extremely loyal, and hardworking. He is a strict soldier when it comes to his duties and leads his own subordinates by example, earning their respect. While not the most intellectually gifted member of Mustang's team, he compensates with common sense, cleverness, and a high aptitude for combat, often providing a sarcastic and grounded perspective to counter the more extreme plans or personalities of his comrades. A recurring and notable weakness is his terrible luck with romantic relationships, which he struggles to maintain due to his dedication to his work and his loyalty to his commanding officer.

As an officer under Roy Mustang, Havoc's primary role is as a field operative. He is one of the few people who is privy to Mustang's secret ambition of becoming the Führer of Amestris to enact change from within. His combat style is characterized by a "shortstop" role, where he uses dual pistols or a shortened carbine rifle, making him highly effective in narrow, indoor close-quarters battles where he can rapidly penetrate enemy lines for disturbance and assault missions. His key relationships are primarily with his fellow subordinates in Mustang's unit, including Heymans Breda, Vato Falman, and Kain Fuery, with whom he shares a strong camaraderie. His bond with Mustang himself is profound, built on mutual trust and respect despite the colonel's habit of piling on work and forcing transfers that complicate Havoc's personal life.

Jean Havoc's role in the story becomes significantly more prominent and tragic during a mission to capture the serial killer Barry the Chopper. While on surveillance in Central City, he begins dating a woman named Solaris, who is secretly the Homunculus Lust in disguise. Lust approaches him to gather information on Mustang’s activities, but her plan fails because Havoc is resolute in his professionalism and never reveals any military secrets, not even to a romantic partner. When Lust's true identity is revealed, Havoc engages her alongside Mustang in a fight at Laboratory 3. Despite a moment of ingenuity where he uses his cigarette lighter to provide a spark for Mustang's alchemical flames, Lust severely wounds him by impaling him through the abdomen. The attack severs his spinal cord, leaving him paralyzed from the waist down.

The psychological impact of this disability is severe, and Havoc initially loses his will to fight, shouting at Mustang to leave him behind and not waste pity on a broken pawn. However, Mustang’s refusal to abandon him and his own inherent resilience allow him to recover his determination. Accepting a medical discharge from the military, he returns home to help run his family's general store. Even from this position, he remains fiercely loyal to his former colonel. On the Promised Day, when Mustang launches his coup to take control of Central, Havoc provides critical support by covertly supplying an armored truck loaded with weapons and ammunition under the guise of "Havoc General Store," a service he cheekily describes as delivering everything from rubber bands to state-of-the-art tanks. His final development involves his physical recovery, which is depicted differently across adaptations. In the manga epilogue, he is shown undergoing physical therapy to regain the use of his legs, while in the second anime adaptation, he is fully healed when Doctor Tim Marcoh uses a Philosopher's Stone to repair his spinal injury, allowing him to stand on his own two feet again. Despite his injury and change in career, Havoc exemplifies the enduring loyalty and quiet strength of a soldier who continues to support his cause by any means necessary.