The character known as Gian is born Takeshi Goda, a name that appears rarely as he is almost exclusively referred to by his nickname, which is derived from the English word "giant". He is a ten-year-old boy recognized immediately by his large, robust build, which is often interpreted as a combination of strength and bulk, along with his short black hair and tan skin. His typical outfit varies slightly across different versions of the story but is most frequently an orange shirt, making that color a signature element of his visual design.

At the heart of Gian's personality is a profound contradiction. On the surface, he is the neighborhood's primary bully, ruling the local children through physical force and a quick, violent temper. He is notorious for taking toys, books, or anything else he wants from other children under the pretense of "borrowing" them, a philosophy encapsulated in his personal motto: "What's mine is mine. What's yours is also mine". This behavior is most frequently directed at his classmate Nobita, who is a regular target of his aggression and theft. However, despite this cruel exterior, the series consistently reveals that Gian possesses a strong sense of loyalty and a good heart, particularly when his friends face genuine danger. This duality is most apparent in the feature-length films, where he often sets aside his bullying to become a courageous and dependable ally who refuses to abandon those in need.

Gian is driven by several powerful and often comedic motivations. One of his greatest passions is singing, a hobby in which he has an unshakeable and completely misguided confidence. He genuinely believes himself to be a great vocalist and frequently forces the neighborhood children to endure his horrendous concerts, which are so terrible they cause physical pain and nausea to his audience. Equally disastrous are his attempts at cooking, which he also serves to others with unwarranted pride. Beyond these creative endeavors, he is the self-appointed captain and founder of the local baseball team, named "The Giants" after himself. He is fiercely competitive and athletic, and he often blames his teammates, especially the unskilled Nobita, for the team's frequent losses.

Gian's key relationships are central to his character. He is often accompanied by Suneo Honekawa, a wealthy and conniving boy who acts as his sycophantic sidekick. While they appear to be close friends, the dynamic is built on Suneo's fear and desire for protection, and Gian does not hesitate to bully him as well. His relationship with Nobita is the most complex and deeply explored. While Gian bullies Nobita relentlessly, he also paradoxically depends on him as a member of his team and a constant presence in his life. In moments of true crisis, Gian's underlying care surfaces, and he has been shown rescuing Nobita from danger, expressing concern for him when sick, and even holding his hand to prevent him from falling. Shizuka Minamoto is treated differently; while she is also subjected to his concerts and cooking, Gian rarely bullies her physically, possibly because she is a girl, and he generally listens to her when she tells him to stop his aggressive behavior.

The most significant figure in Gian's personal life is his younger sister, Jaiko, for whom he has a powerful and protective affection. He is deeply devoted to her and her dream of becoming a professional manga artist, often going to great lengths, including stealing Doraemon's gadgets, to help her achieve her goals, even if his help is sometimes overbearing and unwanted. In stark contrast stands his mother, who runs the local grocery store. She represents the only force that Gian genuinely fears, and he will quickly abandon any act of bullying or disobedience at the mere sound of her angry voice, a weakness that Nobita and Doraemon frequently exploit to their advantage.

Throughout the series, Gian displays moments of unexpected development where he questions why his friends avoid him. After receiving a stern lecture from Doraemon about his behavior, he has shown genuine remorse and a desire to become a better person, though these attempts at reform are often quickly undone by his own uncontrollable temper or by the mocking reactions of his peers. In glimpses of the future, this growth is shown to be successful, as he is portrayed as having overcome his bullying nature to become a responsible and good father.

Gian's notable abilities are primarily physical. He is, by a wide margin, the strongest and most athletically talented child in his peer group, excelling in sports, especially baseball. While his terrible singing is a source of comedy in daily life, it is presented as a unique, almost weaponized ability in some of the feature films, where the sheer power of his voice can be used effectively against enemies. This combination of brute strength, hidden loyalty, and comedic flaws makes him a multifaceted character whose presence is essential to the story's dynamics.