If you mean steven, the champion, he lives in the house in the upper left corner of the island.
in mossdeep city
not
How do you unlock the door in the old man's house who lives on mossdeep city on Pokemon Ruby
you have to
with your foot
mossdep city really north west corner
You catch staryu in Mossdeep city right behind Stevens house.
in mossdeep city
You can't, You get dive from Steven in his house in Mossdeep.
In Pokemon Ruby/Sapphire/Emerald in Mossdeep City.
You go to Steven's house in Mossdeep city. He's northwest of the Pokemon Center. When you enter, he'll give you HM08. HM08 (Dive) is exclusive to Pokemon Ruby and Sapphire and is obtainable in Mossdeep City from Steven who resides there. Steven
There around the hunters house west from mossdeep city. You need the HM dive to find them.