Generation I is the only generation not to feature the paired versions' mascots on the title screens, but instead includes the first evolutionary stages of two starter Pokémon. Generation I is the only generation without a playable female character, although evidence suggests plans for an intended female player character.
Details in the Hoenn- and Kanto-based games hint that the storyline of Ruby, Sapphire, and Emerald is contemporaneous with that of FireRed and LeafGreen (and due to this, contemporaneous with Generation I as well), placing Generation III three years before Generation II and Generation IV, themselves contemporaneous.
As in other regions, the Kanto region holds a number of Gyms located throughout the area. In the Generation I games and their remakes there are a total of eight Gyms. In the Pokémon Anime, the main character Ash, battled at eight Gyms as well. However, as seen with several characters' Badges...
Like other regions, the Johto region has its own set of eight gyms (the other eight from the Kanto Region can be accessed later on) that trainers can battle to get badges and to be able to face the Elite Four. The Johto Gym Leaders are Falkner, Bugsy, Whitney, Morty, Chuck, Jasmine, Pryce, and Clair.
Much like Generation I's version of Kanto was featured a second time in Generation III, Pokémon HeartGold and SoulSilver caused Johto to be featured a second time in Generation IV. Starter Pokémon Much as Kanto's Generation III starters were the same as in Generation I, Johto's starters have not changed.
Much like Generation III remade the Generation I games, the Generation II games also received much anticipated remakes in the form of HeartGold and SoulSilver, and through details revealed in the five main games, Generation IV is thus known to be contemporaneous with Generation II, occurring three years after Generation I and Generation III.