Brock wanted to be the greatest Pokémon Breeder (he is now following his destiny as a Pokémon Doctor), and gives up his title of Gym Leaderafter Ash won his first Kanto League Gym Badge from him. He was first seen taking care of his nine siblings.
Brock's most notable feature about his appearance is that his eyes naturally appear closed. The rare times people see them open are when they are forced open unnaturally: from a hit with Charmander's Flamethrower in The Ninja Poké-Showdown, when being hit in the back of the head by Arbok's tail in Who Gets to Keep Togepi?, and when he makes a face for Larvitar in A Crowning Achievement. This has been the center of fan attention for a long time. He also has tan skin, notably darker than the skin of any other major character in the anime, until Iris in the Best Wishes series. Brock, along with Tracey and Cilan, are the tallest of Ash's traveling companions, and the closest to looking like an adult. Next to actual adult characters, however, it is clear that he is still a teenager. Not counting temporary outfits, he has worn three different outfits over the span of the anime, all of which have had the colors orange, green, and brown, with blue shoes.
Brock is considered the most mature, wise and level-headed of the main characters, and he is arguably the most intelligent character as well. He often acts as an older brother and caretaker to the other characters and a voice of reason in disputes. He will usually place others before him and will help and support his friends even against his better judgment or at his own expense. While he is not shown to battle often, he can understand the situations and strategies in any Pokémon battle, and often explains them to the other characters, probably due to the fact that he was once a Gym Leader. His wisdom is possibly derived from how observant he is; he can tell just by sight how a Pokémon is feeling. Brock always carries books and maps with him, and thus is usually the character who knows where the group is headed and what they can do when they get there, though in the Advanced Generation series this role was mostly taken over by Max, who owns a PokéNav. He also carries a lot of other supplies, such as Potions, Pokémon food, and a set of cookware, as well as practical tools like a brush and pocket knife; in The School of Hard Knocks, the extent of his preparedness and comically large capacity of his bag was demonstrated, as he pulled out a table and full tea set out of his backpack. He is a domestic, and grooms not only his Pokémon but also those of his friends with whom he travels. He handles all the cooking and cleaning for his friends.
Despite this, all his maturity and rationality leaves him completely at the sight of a beautiful woman. Brock has a desperate need for female companionship which grows worse as he fails to gain it. He will do anything and everything he thinks will impress women, which inevitably ends with his heart being broken every time. A few women have shown interest in him as well, such as Wilhelmina, Temacu, Natalie, Lucy, Holly, Autumn, Narissa and Lizabeth, but most do not notice him or are not interested. No matter how many times he is disappointed, though, Brock remains determined to find a girl to start a relationship with, and has indicated several times he would stop traveling with Ash and stay with the girl if this happened. This behavior tends to wear on the nerves of other characters, and Misty and Max have both commonly dragged Brock away from women by his ear. Some of Brock's own Pokémon, most notably Croagunk, have attacked him for getting too flirtatious with women. His goals have played a passive role in his character's activity and development, and his role has generally been one as support for other main characters, usually contributing more in terms of wisdom and comedic antics than the action of the series. Unlike other characters, who aspire to achieve and excel in competitive fields like Pokémon training and Pokémon Contests, his aim to become a great Pokémon Breeder is a quiet one and thus does not get showcased frequently. This caused him to question if he was actually pursuing his dreams like his friends were near the end of the Diamond & Pearl series, and ultimately lead to him deciding to become a Pokémon Doctor instead. His other goal, to find a girlfriend, is similar to Team Rocket's quest to capture Pikachu in that both are for comedy and thus doomed to fail.
After Ash loses to Brock, a stranger offers to help make his Pikachu stronger. Pikachu (after being hooked up to a local hydro-power station) becomes stronger and manages to defeat Geodude, but Onix remains too strong. Onix hasPikachu in a body bind; however, Pikachu's previous electric attack ravaged the gym, which set off the sprinklers, weakening his Onix. Ash declines the badge on the grounds that he unfairly beat Brock, but Brock later catches up to him and presents to him the badge, saying that he wants Ash to fulfill his dream of becoming the best. The stranger that first helped Ash reveals himself to be Flint (Kanto), and that he is Brock's father. Flint has a tendency to keep people in the dark about who he is.
Brock is now free to train himself, and joins Ash and Misty on their journey. Since then, he travels with Ash and Misty on his many adventures. In the Orange Islands series, he leaves the team to join Professor Felina Ivy, but mysteriously returns to Pallet Town when Ash wins the Orange League Championship. When asked what happened, Brock just rolled up into a ball and replied, "I don't wanna talk about it" or "Don't mention that name". This would happen every time someone mentioned Professor Ivy. Rejoining Ash and Misty, Brock travels toJohto, where he continues to help Ash and Misty. Upon the conclusion of the Silver Conference, the three part ways, Brock heading back to Pewter City. It is there (in an episode of Pokémon Chronicles) that he discovers his estranged mother Lola (Mizuho in the original), who, because she is a Water-type Pokémon Trainer, has ruined the reputation of the Gym he defended so long ago and had ended up filling the gym with water (causing Brock to comically freak out and keeps repeating "A LAKE!!!" when he first sees it).
By defeating his mother, he restores the Gym's reputation, and proceeds to leave all his Pokémon (exceptForretress) to his younger brother Forrest, before departing for the Hoenn region, where he catches up with Ashand his two new friends, May and Max.
The group travel across Hoenn and then return to Kanto to participate in the Battle Frontier. The group went their separate ways and Brock met up with Ash in Sinnoh. While there, they meet a new coordinator named Dawn and her partner Piplup, who joins them on their journey through Sinnoh .
During this time, both Brock's father, Flint (Munō in the original, who was also Brock's predecessor as Gym Leader), ran off again, and his oldest younger brother Forrest (Jirō in the original) took the role of Gym Leader inPewter City, as well as the responsibility of caring for his many other younger siblings. Brock is the oldest of ten siblings, with five brothers and four sisters.
Brock is always well-equipped, and is sometimes the voice of reason when Ash and Misty (and later, May and Dawn) get into an argument. He is also hardworking and is always willing to help others. Coupled with his experiences in taking care of others, Brock often prepares food and does most of the chores for the main characters. Brock is also exceptionally good at making food for Pokemon.
At the end of the Pokémon: Diamond and Pearl series, Brock aspires to become a Pokémon Doctor, and work alongside Nurse Joy. After departing from Ash and Dawn, Brock returns home to Pewter City to train to become a Pokémon Doctor.
In the Pokémon: Diamond and Pearl Special Episode 2, he has photos of Ash, Misty, May, Max, Dawn, Piplup, and Pikachu to remind him of how much fun it was traveling with them. He also chooses his brother Forrest to replace him as Gym Leader
In the Black and White Special he encounters Cilan in a small town. He helps treat Pansage after it got hurt fighting a Gyarados. The two form of fast friendship and work together as they help Gyarados. As they part they both realize they never asked for each other's name.