Brock captured Bonsly in the episode From Cradle to Save, while Ash, May, Max and himself were training at a ninja school in the Kanto Battle Frontier. Being much younger than the other Pokémon, Bonsly was portrayed as a needy and child-like, and Brock was often seen bottle-feeding him until he could eat normal food.
Bonsly occasionally took over from Max in getting Brock away from girls. However, rather than pull his ear, Bonsly hit him with a powerful Take Down.
Brock entered Bonsly in a Pokémon Contest in What I Did for Love.
When Brock joined up with Ash in Sinnoh, Bonsly was the only Pokémon he brought with him. In A Staravia is Born!, Bonsly learns the move Mimic, so in Leave It To Brocko, Bonsly evolves into Sudowoodo.
Since its evolution, it has matured and is no longer a crybaby. In fact, it is very upbeat, as seen in All Dressed Up With Somewhere to Go when it recovered from a crushing disappointment almost instantly. It has also shown a significant increase in its power and battling skills. Instead of being needy and heavily reliant on Brock's care, Sudowoodo is eager to help Brock in almost any task. In almost all regards, it has grown from a typical baby Pokémon into a strong adult Pokémon, a true testament to Brock's talents as a Pokémon Breeder. It also has an odd tendency to salute Brock whenever it is called from its Poké Ball.