In Pokémon Red Version, Pokémon Blue Version, Pokémon Green Version (Japan only), and all of their many remakes, he will travel to Pokémon Tower where he will be furious about the recent events that Team Rocket did. Apparently, Team Rocket recently killed a Marowak, which is why the old man is in the tower. Once he entered, Team Rocket held him hostage until you, the player, would come and save him.
Once you would save him, he would give the player a Poké Flute which would allow the protagonist to wake up sleeping Pokémon such as Snorlax. It should also be noted that you need the flute to beat the game.