Hoenn
Before joining Brock's party in episode The Lotad Lowdown, Lotad belonged to a group of Lotad that lived near the Flower Shop between Petalburg City and Rustboro. It was somewhat dense compared to the other Lotad that watered the shop's garden, but thanks to some encouragement from Brock, it was eventually able to water the plants as well. Soon after, it joined Brock's team after rescuing its fellow Lotad from Team Rocket.
Lotad's personality was somewhat similar to that of Misty's Psyduck, although not as frustrating to its Trainer, as Brock is much more patient then Misty was. It usually had a vacant stare about it and was slow to react to the events occurring around it. Nevertheless, it remained a trustworthy Pokémon when called upon to do battle or to aid Brock (its lily pad makes for a handy table). It stood loyally by Brock's side when he nursed an injured Sharpedo back to health in episode Sharpedo Attack!.
During the events of the episode A Mudkip Mission, Lotad rescued some Mudkip, one of which Brock captured. Since then, the two Water types would often be used together, usually to launch a dual Water Gun attack.
Lotad evolved in Take the Lombre Home!, after falling into an empty well. The people of the nearby village claimed Lombre as their "Water Lord," and hoped that it would be able to end the drought blamed on a Solrock. As a Lombre, it continued to be used often alongside Mudkip. Because it looks similar to a sombrero-wearing human, Lombre has performed alongside Brock in his Takeshi's Paradise outfit.
In Once in a Mawile, a Mawile became infatuated with a seemingly uninterested Lombre. Brock wished Lombre to reciprocate so that he could get closer to Mawile's Trainer, Samantha, but Lombre appeared apathetic. Later, while Mawile and Samantha were performing onstage, Lombre searched through Samantha's belongings, discovering a Water Stone. The contact with the Water Stone triggered its evolution into Ludicolo, as well as a change in personality. As a Ludicolo, it now was much more friendly and energetic, and was now willing to return Mawile's affection. Unfortunately for Ludicolo (and Brock), Mawile wanted nothing to do with the fully evolved Pokémon and moved on to other Pokémon, namely a Psyduck. Although surprised, Ludicolo quickly bounced back to its happy state and took Brock with it.
Because of how much his brothers and sisters enjoyed it, Brock left Ludicolo with his family at the Pewter City Gym, as revealed in A Real Cleffa Hanger.
Kanto Battle Frontier
Ludicolo also appeared in Grating Spaces! where it was revealed that Brock's parents took Ludicolo with them on holiday so it could carry their luggage.
As a Lotad, Ludicolo proved to be a bit slower than the other Lotad it worked with. Gradually, Lotad grew to be a high functioning Pokémon, with the help of Brock's encouragement. As a Lombre, Ludicolo proved to be a very happy Pokémon, often cheering for its teammates in battle. In Once in a Mawile!, Lombre showed that it was oblivious to Mawile's advances, proving that it was also quite carefree. As a Ludicolo, it seems to maintain these characteristics and was also returning Mawile's affection, only to be rejected. It got over this quickly however, also proving that it is very upbeat. As seen in Grating Spaces, Ludicolo proves to be a very helpful Pokémon, happily helping Brock's parents with their luggage.