Nurse Joy

Nurse Joy (Japanese: ジョーイ Joy) is a nurse at the Pokémon Centers throughout the various games and in the anime. Nurse Joy heals your Pokémon to perfect health.

Anime
In the anime, the reason that Nurse Joys are all over the place is because they're all related. Not only that, but Joy is their family name and not their actual first names.

Although they all appear identical, Brock is able to tell them apart by little details. This is noted when he can tell the difference between the eyelash length of two different Nurse Joys. Brock has a main crush on Nurse Joy, although he's always interupted by his Croagunk.

Pokémon
Nearly every Nurse Joy in the anime have Pokémon with them at some point in time.

Main
However, some Nurse Joy have individual Pokémon they keep with them.

Trivia
The Joy Family all appear identical as a parody to how character models were recycled and reused in the first Pokémon games. This also applies with Officer Jenny.