Gatz, more commonly known as Guts in most translations, is the central protagonist of the manga Berserk. He is a formidable mercenary and wanderer known by several epithets, including the "Black Swordsman," the "Hundred Man Slayer," and the "Struggler". His life is marked by a constant battle against both supernatural horrors and his own inner darkness.

His origins are nothing short of tragic. Gatz was born from the corpse of his mother, who had been hanged from a tree. He was discovered as a newborn infant lying in a pool of her blood by a band of mercenaries. The mercenary leader, Gambino, reluctantly took him in at the behest of his lover, Shisu, who briefly cared for the child before dying of plague. As a result, Gatz was raised within the violent, uncaring world of mercenaries. His childhood was brutal; Gambino, who became a bitter and abusive guardian, taught him the art of sword fighting but offered no affection. This upbringing instilled in Gatz a fierce will to survive and a deep-seated belief that he was cursed or unwanted, a child who was never meant to be born.

In terms of personality, Gatz is initially presented as a gruff, cynical, and misanthropic individual. His traumatic past has left him with a bleak outlook on life, making him guarded and prone to outbursts of cold, brutal violence. In his early adult life as the Black Swordsman, he is consumed by a vindictive thirst for revenge, becoming anti-social and indifferent to the suffering of others, even using innocent people as bait to achieve his goals. However, this hardened exterior hides a more compassionate and easygoing side that emerges when he is around people he trusts. He is fiercely loyal and protective of his companions, though he often struggles to express these feelings openly. As a personification of perseverance and resilience, Gatz is an ardent detractor of destiny, constantly raging against an uncaring world and the flow of causality that seeks to control him.

His primary motivations have evolved significantly over the course of his journey. For much of his early life, he fought simply as a means to survive. As a young mercenary, he lacked true purpose and sought only to prove his strength and gain validation from others. After surviving the horrific Eclipse, where his closest friends were massacred and his lover was mentally shattered, his driving force became a singular, all-consuming quest for revenge against his former comrade, Griffith, and the demonic God Hand. This desire for retribution eventually gives way to a more profound motivation: the need to protect and cure his lover, Casca, whose mind was broken by the trauma of the Eclipse. This shift from a path of vengeance to one of guardianship marks a critical turning point in his character arc.

Gatz's role in the story is that of the eternal struggler, a man fighting against impossible odds in a dark fantasy world. He is the focal point around which the narrative revolves, initially appearing as a lone monster hunter before his tragic backstory is revealed in an extended flashback. Following the Eclipse, his role shifts from being a member of a merry band to a solitary avenger, and finally to the reluctant leader and protector of a new family of fellow outcasts, including the elf Puck, the young thief Isidro, the former holy knight Farnese, and the witch Schierke.

Key relationships define his existence. His relationship with Griffith, the charismatic leader of the Band of the Hawk, is the most significant. What begins as admiration and friendship curdles into a turbulent rivalry and ultimately a consuming hatred after Griffith sacrifices the band to become a demon lord. His relationship with Casca is another cornerstone. Starting as rivals, they grow to deeply love each other, and her subsequent insanity following the Eclipse becomes the primary anchor for his rage and, later, his salvation. His bond with his mentor, Gambino, was one of abuse and fear, ending in a tragic act of self-defense that haunted Gatz for years.

Gatz undergoes profound character development throughout the series. He transforms from a blank slate of a child mercenary, killing simply to live, into a young man searching for his own dream and identity. After the Eclipse, he devolves into a nihilistic "mad dog" obsessed with slaughtering demons, pushing all human connection away out of fear of losing loved ones again. Eventually, through the simple, persistent companionship of the elf Puck and the responsibility of caring for the defenseless Casca, he slowly begins to open his heart again, learning to trust his new companions and value their lives above his quest for revenge. This journey from a beast of vengeance to a protector is the heart of his character arc.

Notable abilities set Gatz apart from ordinary humans. His most iconic weapon is the Dragon Slayer, a massive slab of iron so large and heavy that no normal man could lift it, let alone wield it as a sword. He carries it on his back and uses it to cleave through both armies and massive demonic apostles. To replace his left forearm, which was severed during the Eclipse, he uses a mechanical prosthetic arm. This arm is a sophisticated piece of equipment that houses a powerful repeating crossbow and a hidden cannon, providing him with devastating ranged options. Later in the story, he acquires the Berserker Armor, a cursed suit of armour that enhances his physical strength and pain tolerance to superhuman levels, allowing him to fight even when grievously wounded. The armor has a tremendous cost, as it unleashes his inner beast, a feral "Black Wolf" or "Hellhound" personifying his rage, which threatens to consume his consciousness and turn him into an uncontrollable berserker who cannot distinguish friend from foe. His sheer willpower, honed by a lifetime of suffering and struggle, remains his greatest and most defining asset.