From Bulbapedia, the community-driven Pokémon encyclopedia.
Brian Campbell (Japanese: ブライアン キャンベル Burian Kyanpuberu) is a somewhat professional Pokémon Trainer currently traveling throughout Unova. His goal is to make the most powerful Pokémon team. His first Pokémon, Totodile, was given to him by Professor Elm in the Johto region. He has since traveled throughout the first four regions, and is now at the fifth.
Brian's main goal in life is to build the strongest team of Pokémon, able to beat anyone. Brian began his journey at the age of 10 as a warm-hearted and well-intentioned but stubborn, rash and amateurish Pokémon Trainer. He was forced to accept the bold Totodile from Professor Elm as his starter Pokémon because it had attacked the other trainers who tried to take it, making it the only one left. For months the Totodile had been rude and arrogant, but one day, a swarm of Beedrill attacked them. Totodile tried to protect himself, but was badly injured. In an attempt to keep Totodile safe, Brian ran straight into the swarm and yelled at Totodile to run away. Totodile instead stood up and fired an immensely powerful Hydro Pump at the swarm, and they fled. With that attack, Totodile evolved into Croconaw. From then on, Croconaw and Brian have had a close relationship.
However, from that point, Brian still had a lot to learn about becoming a Trainer. His first Pokémon was caught by luck, he knew absolutely nothing about battling, and was hesitant to admit it whenever he was wrong. Many of his first Gym badges were given to him merely out of pity rather than claiming an actual victory in battle over the Gym Leaders; of his first three gym battles, only his victory over Jasmine was an actual victory.
Over time, Brian's dedication to his goal paid off. After earning his first eight badges he went on to compete in Kanto, getting the eight badges there, even beating all members of the Elite Four and even the champion. He then went to Hoenn and Sinnoh, where he did the same. He was especially determined in these regions due to their legendary Pokémon; specifically, Arceus, Deoxys, Giratina, Dialga, and Palkia. Arceus was his favorite, and still is, but he couldn't get close enough to battle it, despite it flying near him. The other 4 never revealed themselves to him, but he did still love being there.
Later, after becoming champion of Kanto, Hoenn, and Sinnoh, he went back to Johto to do the same. He beat the Elite Four easily, but Lance wasn’t as easy. He managed to get her down to her last Pokémon, Dragonite. Brian used all of his Pokémon to try and win, but it came down to Croconaw and Dragonite, who had 1/10 the HP. Dragonite attempted to use Hyper Beam, but aimed at the wrong target. Seeing this aimed at Brian, Totodile used the same move it did when Brian first got it and protected it from Beedrill. A huge Hydro Pump filled the arena, and after the smoke and water cleared, Dragonite was knocked out, with an exhausted Feraligatr standing near it. With that, Brian became the Champion of the first four regions, heading into the fifth, Unova, but not without catching some more Pokémon.
He has traversed much of the Pokémon world and has thus far participated in four Pokémon League regional competitions, but he is still learning new things about Pokémon all the time.
Lately, he has left Unova for a brief search through the known and unknown world looking for an unrecorded Pokémon that he saw in a mysterious dream. He claims that it is the child of Arceus and was sent to Earth to rid the world of evil.
Over the course of his journey, Brian has captured a number of Pokémon, but he has focused on them individually, and most have helped him win a badge somewhere.
With Professor Oak/Professor Rowan