When Brock is first introduced in the Pokémon anime, his goal is to become a Pokémon Breeder, a job which involves a lot of intensive care and study. In his most recent appearances, however, Brock is shown to have become a Pokémon doctor. So what happened to change Brock's goals?
Pokémon Breeders are a trainer class from the games, and are usually characterized by having larger parties of Pokémon with greater variety, but at a lower level. However, these Pokémon Breeders only began appearing in Ruby and Sapphire, long after Brock declared his goal. The inspiration for Brock's Pokémon dream is most likely dog breeders, who will raise puppies with the intention of having them compete in dog shows, where performance is judged on ability and how closely they match "breed standards," as decided by the judging organization. Brock's concern over keeping his Vulpix's coat healthy and soft, for example, may be due to one such standard.
Brock kept his goal as Pokémon Breeder for a long time. The introduction of Pokémon contests in Ruby and Sapphire added a new element to the games which more closely matched how dog shows work, but the goal of succeeding at Pokémon contests was given to May, and later Dawn. This Orange Islands variant Butterfree in "Poké Ball Peril." Brock returned home to Pewter City while he studied to become a Pokémon Doctor, finally leaving the show after 650+ episodes.
Where Brock Stands Today
In later appearances, Brock is shown to have gone to Pokémon med school, and interned in Johto. Brock made use of his new doctor skills in his return in Sun and Moon, where he diagnosed Lillie's Vulpix with motion sickness, and later treated a Yungoos and a baby Kangaskhan when he traveled to Alola. Brock was also shown not to have let his skill as a trainer get away from him, having mastered Mega Evolution and posed a challenge to Ash's new friend Kiawe. In Journeys, Brock is shown as a full-fledged Pokémon Doctor, working at the Oreburgh Pokémon Center in Sinnoh alongside his Blissey and Croagunk. He helps Ash once more to stop Team Galactic before returning to his work at the Pokémon Center, and is shown watching Ash's final victory in the World Coronation series.
Brock is currently set to return for Ash's farewell miniseries, Pokémon: Aim to Be a Master, alongside Misty. Hopefully, he'll get to show off some of his Pokémon medical knowledge throughout whatever adventures lie ahead.
