In Pokemon Red/Blue, the player journeys through Kanto, defeating Gym leaders along the way to obtain the badges required to face the Elite Four and Champion. A typical journey starts at Pallet Town to obtain their starter Pokemon. After some adventuring, the player tackles the first gym they encounter, beating Brock to get the Boulder badge. Subsequently, they beat Misty in Cerulean City for the Cascade badge then Lt. Surge in Vermilion City for the Thunder badge
Old Revision
In Pokemon Red/Blue, the player journeys through Kanto, defeating Gym leaders along the way to obtain the badges required to face the Elite Four and Champion. Assuming the player tackles the Gyms in the order they encounter them, a typical journey starts with beating Brock to get the Boulder badge, Misty in Cerulean City for the Cascade badge then Lt. Surge in Vermilion City for the Thunder badge.
Correction
Um actually … The first Gym that the player encounters is in Viridian City, which is hosted by Giovanni, who is not available at that point in time.
Fantastic fix that clears it up and makes the correct answer very clear!