Viridian City

Viridian City is the first major city in the Kanto region generations. It lies directly north of Pallet Town and directly south of Pewter City. It also lies to the east of Victory Road.

Pokémon academy
The Pokémon academy is a school which teaches the basics of Pokémon training, such as status effects. It serves primarily to help inexperienced trainers.

Trainer House
The Trainer House replaces the Pokémon academy in later games and serves as a battleground. The trainer Cal can be found here and can be battled daily.

Viridian Gym
The Viridian Gym is the first gym many new trainers come across. It is situated near a narrow ledge which can make navigation difficult, as a single slip can send them running back the long way round. In the Kanto region generations, the gym is initially locked and will force players over the ledge when they try to enter.

Upon defeating Team Rocket in Saffron City and obtaining every other badge, the gym becomes accessible. The gym leader turns out to be none other than Giovanni, the head of Team Rocket who was elsewhere supervising his criminal empire. Defeating him causes him to admit defeat, disband Team Rocket and give the protagonist the Earth badge which allows them access to Victory Road.

In the sequel generations, Blue runs the gym instead.

Giovanni
Giovanni is the boss of Team Rocket and serves as the final challenge to face Victory Road as Viridian Gym leader. He typically uses Ground-type Pokémon that know Earthquake, but in the randomized FireRed runthrough, used Fighting-type Pokémon instead. He installs his favored spinning traps in his gym. After he is defeated, he disappears and is not heard from again.

Blue
Blue took over as Viridian Gym leader following Giovanni's disappearance. He does not favor any particular style but instead uses a team composed of Pokémon from his time as temporary champion. In Crystal, aside from Clyde he was the only occupant of the gym and the only one to fight, having removed the spinning traps. In HeartGold he had other trainers to fight alongside him and had reinstalled the spinning traps in a trickier design. He also went from being typeless to being a Flying-type gym leader.

Old Man
The Old Man is a grouchy old man lying in the middle of the road because he hasn't had his coffee. After having his coffee, he will show the player how to catch Pokémon. He is also the source of an infamous item duplication glitch.