The Kanto Pokemon Gym Leaders are among the most well known in the whole franchise. Brock and Misty famously became part of the main cast in the anime, and plenty of the other Gym Leaders like Sabrina or Giovanni are pretty famous.

Erika on the other hand feels like one of the odd kids at the party. She is not very memorable and plays a minimal role in both the games and the anime.

She is the leader of the Celadon City gym and focuses on using Grass type Pokemon. I love the grass type, but being a type with 5 weaknesses, many of which common in the region, makes Erika rather trivial for most players.

Pokemon Red, Blue, Yellow, Fire Red, Leaf Green

Erika is the fourth gym leader the player encounters and uses a team consisting of 3 Pokemon. Those being a Victreebel, a Tangela, and a Vileplume. To be honest they did the best they could with the grass types available. Tangela can wrap stall you in the Generation 1 games, and the other two can spread status and at least be annoying. Still, any Pidgey or Fearow or really any Fire, Flying, or Psychic type will make quick work of her team.

After beating Erika she will hand you the Rainbow badge and the TM for either Mega Drain or Giga Drain, depending on the game. She is not seen or heard from after this point.

Pokemon Yellow

I wanted to quickly highlight that her team in Yellow is strangely worse than the other Kanto games. Her Victreebel and Vileplume are only a Weepinbell and Gloom respectively. I suppose this is because Yellow is modeled after the anime, in which she uses Gloom, but it's a weird game design choice to randomly nerf an already easy gym leader.

Pokemon Gold, Silver, Crystal, Heart Gold, Soul Silver

Erika retains her Gym Leader position in Celadon City in the Johto games, taking place two years after the Kanto games. She can be fought in the Post game, when the player travels to Kanto.

In the Gen 2 and Gen 4 games she still uses her Tangela and Victreebel, but ditches her Vileplume for the newly added Bellossom. She also adds a Jumpluff to her team. By this point in the game every trainer should be able to beat her pretty handily.

In Pokemon Heart Gold and Soul Silver, Erika can be rematched after calling her on specific days of the week. She, like the other gym leaders, will appear in Olivine City after this, where the player can challenge her again. She evolves her Tangela into a Tangrowth, and further adds a Shiftry and Roserade to her team, finally obtaining 6 Pokemon of her own.

Pokemon Black 2, White 2

Erika, like all the other gym leaders, can be challenged in the Pokemon World Tournament. She can appear in a few different challenges, like Grass Specialists, Kanto Specialists or the general competitions. She will use a plethora of Grass type Pokemon from different generations.

She is not seen at any other point in the game.

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And those were all of Erika's main line game appearances. She will also appear in some spin-offs like Stadium or Pokemon Masters (where, funnily enough, she was the character with the most Sync Pairs for quite a while. I suppose she is pretty popular in Japan, given her Kimono design).

I do like Erika, but she is pretty boring as far as gym leaders go. If it weren't for her being a Kanto gym leader, she'd be forgotten among the masses. Still, she's the only Grass Gym Leader until Gardenia in Sinnoh, who admittedly puts up much more of a fight.