Once you obtain all seven Kanto badges in addition to the eight Johto Badges, talk to Blue on Cinnabar Island. He'll then go to the Viridian City Gym to await to battle you.
In the original Silver game, the gym leader was Blue and you would find him at Cinnabar island. After meeting him there, you can go back to the gym and fight him.
HeartGold/SoulSilver-Viridian City. You have to have the other 7 kanto badges and then find him on Seafoam islands. He will go back to the gym in Viridian and you can fight him.
He Doesnt Come Back Hope I Helped :D
In the beginning of the game, he isn't there. Towards the end, you will find his rival on cinnabar island by himself. After you talk to the rival, he leaves to go back to viridian. Fight the cinnabar gym leader, go back to viridian and the gym leader should be there. The man you talk to on Cinnabar Island Isn't the gym leader, but his rival. After you speak with his rival on cinnabar, the gym leader reappears in viridian. You have to fight and beat the cinnabar gym leader first.
he disappears and never comes back
You obtain the Earth Badge by defeating the first seven gyms, and then going back to Viridian and taking on the mysterious gym leader there (although we all saw it coming as to who was the leader of Viridian Gym)
The 16th gyme leader is first on cinnibar island talk to him to make him go back to the viridian city gym.
don't you just go back to Viridian and defeat Giovanni
The Viridian Gym leader is Blue he is hanging out on cinnabar island (reached by surfing south from pallet town) he tells you he will only battle someone who has the other seven gym badges. This means you have to keep surfing east until you reach the Seafoam islands inside climb the ladder and you will be brought to the gym of Blaine (the fire trainer). After defeating Blaine go back to cinnabar island and speak to Blue he will then return to his gym back in Viridian city Hope I've been helpful
defeat all the other gym leaders
go south from pallet town and go to cinibar island there will be the 8th kanto gym leader but you need 7 gym badges to get him back to virdian city so you go to seafoam islands(east from cinibar in the sea) and go up the ladder then you will fight blaine he has fire type Pokemon then go back to cinibar and show blue(8th gym leader)then go back to virdian city and challenge blue
beat the other 7 gyms in kanto and talk to the 8th gym leader on cinnabar island. he will leave and go back to the gym