Dewford town.
fortee city
Lavaridge town
Find cut
He is the sootopolis city gym leader.
It's Fortree City
go to mosdeep city and it will be to the north of it
The 6th Gym Leader In Pokemon Ruby Destiny is in Down Pour City
Fortree City ( Feather Badge ) Leader's pokemon: Altaria, Swellow, Skarmory, Pelipper
If you mean "Is Juan the leader in Pokemon ruby?", then no. It's Wallace who's the leader. Juan is leader only in Pokemon emerald. The champion is Wallace in Emerald, but Steven is the champion is Ruby and Sapphire.
He's on Slateport City's museum, second floor.
go up north to the next city and earn the gym badge there
Mauville City But you have to beat the city's gym leader before you can turn off the generator in New Mauville City