She was voiced by Kyoko Hikami in the Japanese version, she was also voiced by Leah Applebaum in the English version.
Erika has short black hair (blue in the anime), fair skin, and brown eyes. She has cut bangs, and wears a hairband.
As a nod to the nation of the video games' origin, Erika always dresses in tradition Japanese garments, consisting of elegant kimonos, which vary in color from pink (Pokémon Red, Blue, Green, and Yellow), yellow (Pokémon FireRed, LeafGreen, HeartGold, and SoulSilver), or green (Pokémon: Let's Go Pikachu! & Let's Go Eevee), but always features an obi (sash). She pairs the kimono with Japanese sandals known as Zōri and socks known as Tabi.
Being an elegant lady, Erika is kind, calm, and modest. She cares deeply about Pokémon, and only collects ones that she finds attractive (particularly Grass-Type Pokémon). Unlike most Gym Leaders, she does not get overly upset whenever she is defeated, rather finding it more satisfying to see how far the player has gone in demonstrating their skill in battle.
According to a note found inside the Celadon City condominiums, Erika is known to have habit of dozing off in her gym, implying that she either has narcolepsy or is frequently exposed to sleeping powder by the Pokémon in her gym.
In Pokémon HeartGold, and SoulSilver, it is revealed that she has a slightly more mischievous side, in which she spreads gossip around about the other Gym Leaders, particularly Clair.
In the games
Erika is the fourth gym leader the player meets in chronological order. Her gym is filled with entirely-female trainers and requires the player to have at least one Pokémon that knows the move "Cut" in order to gain access to the center of the gym, where she resides. Erika's team consists of a Victreebel, a Tangela, and a Vileplume.
Upon defeating her, Erika will award the player the Rainbow Badge and give them either TM21 "Mega Drain" in the Generation I games, or TM19 "Giga Drain" in the Generation II and III games.
In the Anime
Erika is first seen in episode 26 of the Indigo League series "Pokémon Scent-sation!". She is revealed to be the manager of a perfume shop in Celadon City. After Ash insults the perfume inside her shop, she bans him from the shop. She then also bans him from the gym as a result because of the fact she is also the Gym Leader, making Ash unable to obtain the Rainbow Badge.
Determined to gain the Rainbow Badge one way or another, Ash disguises himself as a girl and infiltrates the gym, before revealing his true identity once fully inside. Despite the fact that he was banned from the gym, Erika agrees to battle him, but their battle is cut short when Team Rocket sets Erika's gym on fire. Erika and Ash team to save the gym, with Erika returning all the Pokémon inside the gym back into their Pokéballs, while Ash extinguishs the fire with the help of his Squirtle. Afterwards, Erika thanks Ash for saving her gym and rewards him the Rainbow Badge for his bravery.
In the Manga
Erika firsts appears in "Blame It on Eevee", where she tasks Red to locate and capture a mutated Eevee created by Team Rocket that is able to transform between its three elemental forms and back uncontrollably. Upon returning, Erika shocks Red by ordering him to kill the Eevee, Red refuses, accusing her of being cruel, only for her to reveal that she is not in fact evil, and wishes to save the Eevee's life.
Later on, she challenges Red to a battle and defeated him. Despite the fact that he lost, Erika decides to give him the Rainbow Badge as she sees great potential in him.
Erika, alongside the other good gym leaders Brock, Misty, and later on Blaine teamed up with Red to help defeat Team Rocket, which consisted of not only Giovanni, but also the other, evil Gym Leaders Lt. Surge, Koga, and Sabrina, as well as all members of the Elite Four to save the Kanto region from being conquered by Team Rocket once they had enough energy to fuel their amplification device. Despite having a disadvantage at first, the good gym leaders and Red ultimately manage to defeat all of the members of Team Rocket and the Elite Four, thus returning the Kanto Region back to its former state.