If you're talking about the guy blocking the path to Sunyshore city in diamond and pearl, you have to defeat Team Galactica at the top of the mountain, beat palkia, etc. After that the guy is gone.
You Don't Wanna Know
go to the Pokemon league. there is a room where a guy "checks" to see if you have all 8 badges. in that room, there are these 2 guys blocking two paths. the guy on the left is blocking mt.silver
he is in victory road.
you need the natonal pokedex
Defeat Team Galactic on Mt. Coronet.
You have to get all eight gym badges
You Don't Wanna Know
To move the guy blocking Mt. Silver , beat all 16 gyms and talk to Prof. Oak
In Pokémon Glazed, to move the guy blocking the path on Route 36, you need to find and defeat him in a battle. After defeating him, he will move out of the way, allowing you to proceed. Make sure your Pokémon team is prepared for the battle, as he may have a strong team.
In Pokémon Y, to get the guy blocking the door to Route 14 to move, you need to defeat the Gym Leader at Shalour City and earn the Cliff Badge. After obtaining the badge, return to the door, and the character will move, allowing you to access Route 14.
Go around. You have to get to Viridian City to make him move. after beating the elite 4, take the S.S. Anne (or whatever it's called) in Olivine to Kanto.
No you cant
Yes, he is in that cave you see right above Cerulean city. The only problem is the guy blocking it is only going to move after you beat the Pokemon league.
go to the Pokemon league. there is a room where a guy "checks" to see if you have all 8 badges. in that room, there are these 2 guys blocking two paths. the guy on the left is blocking mt.silver
he is in victory road.
No one is blocking the way to the Lake of Rage. There is one person blocking the Gym and another blocking the way to route 44.
The guy blocking the cave is Cyrus and he is in spear pillar after you meet him the first time but you need 7 badges to get to spear pillar