Brock is originally the Gym Leader of Pewter City, a position he holds as the eldest of ten siblings after his father, Flint, left home and his mother, Lola, also departed, leaving him to care for his five brothers and four sisters on his own. His primary aspiration is to become the world's greatest Pokémon Breeder, a goal rooted in his nurturing nature and desire to care for Pokémon rather than simply battle with them. This dream is what initially leads him to give up his Gym Leader title to travel with Ash Ketchum and Misty after Ash earns his first badge.

In terms of personality, Brock is consistently portrayed as the most mature, level-headed, and domestic member of the main traveling group. He is hardworking, patient, and acts as a voice of reason when his friends argue, often mediating disputes between Ash and Misty or other companions. He takes on the role of caretaker, handling almost all the cooking and cleaning for the group, and he is always well-equipped with supplies, maps, and cookware. A notable and recurring trait is his immediate and enthusiastic infatuation with almost every attractive girl he meets, typically Nurse Joy or Officer Jenny, which usually ends with him being forcibly dragged away by the ear by a frustrated companion like Misty or Max.

Brock's role in the story is largely that of a mentor, supporter, and coach. While he is a capable trainer and former Gym Leader, he is often depicted as less focused on his own battling and more on helping Ash and others. He frequently provides strategic insights during battles, explaining complex situations to newer members of the group like May and Max. His role is pivotal in Pokémon Chronicles, which follows his adventures after parting ways with Ash and Misty following the Johto region. In this series, he returns to his home in Pewter City and discovers that his estranged mother, Lola, has returned and transformed the Pewter Gym from a Rock-type gym into a Water-type gym, completely ruining its reputation. He challenges and defeats his mother in a battle to restore the Gym's honor, after which he leaves all of his Pokémon except Forretress in the care of his younger brother, Forrest, before setting off to rejoin Ash in the Hoenn region.

Key relationships are central to Brock's character. He serves as a surrogate parent to his nine younger siblings, a responsibility that shaped his caring and responsible nature. His relationship with his father, Flint, is complicated by abandonment, but Flint eventually returns to take over the Gym and family duties, freeing Brock to travel. His relationship with his mother, Lola, is tense upon her return, as her actions directly oppose his life's work, but the conflict is resolved through their battle. His friendship with Ash is a cornerstone of his travels, acting as a steadfast supporter and brother figure. A significant and mysterious relationship is with Professor Ivy from the Orange Islands, whom he briefly left the main cast to assist; he later returns to Ash and Misty but becomes physically ill and refuses to speak about his time with her, simply saying, "Don't mention that name!".

Brock undergoes notable development over time. While he begins as a Gym Leader with a dream of breeding, he eventually evolves his career goal. After traveling with Ash through the Hoenn and Sinnoh regions, he decides to return home to study and train to become a Pokémon Doctor, working alongside Nurse Joys, while still retaining his deep knowledge of Pokémon care and breeding. His notable abilities include an exceptional talent for cooking food that is appealing to both humans and Pokémon, a deep practical knowledge of Pokémon injuries and treatment, and a keen strategic mind for analyzing Pokémon battles. Despite his infatuations, he is rarely seen succeeding in romance, and his persistence in the face of constant rejection becomes a defining character trait.