Legendary pokemon

Answer from: Trixman612
Entei check map raikou check map suicune culerean cape after all other it appears at ho-oh bell tower after getting clear bell and rainbow feather latias check map after talking to steven after getting copycats doll at pokefan club lugia whirl island after getting silver feather

Answer from: Champion Ash
Mewtwo:Beat all 16 gyms and enter Ceruleon cave.Lv.70. Entei & Raikou:Enter the Burned tower head down the lader Entei Raikou and Suicune will run to random places in Johto.Lv.40 Lv.40.
Suicune:Suicune will run to varius locations but will not be shown on the map it will end up at Cerulian Cape.Lv.40.
Latias:Latias will start roaming around after you get copycats doll from the fat guy in the fan club.Lv.35. Kyogre:Kyogre will appear in the tower in the tower just a little past Cianwood city after defeating Red and obtaining the Bleu Orb.Lv.50.

Answer from: Ratchet K.G
Well, let's see.

Mewtwo: Cerulean cave after beating elite 4.
Entei: Roaming Johto.
Raikou: Roaming Johto
Ho-Oh: main legendary pokemon, Bell tower.
Lugia: Whirl islands when you get the silver feather AND beat elite4
Kyogre : Obtain blue orb and go to mystery cave
Latias: She will roam Kanto after you receive it from Steven in the PKMN fan club.
Suicune: Follow it until it ends up at route 14 in kanto.
Zapdos: Find it in Kanto after beating champion
Articuno: Find it in Kanto after beating champion
Moltres: Find it in Silver Cave after beating champion
Latias: Only in SoulSilver Trade.
Groudon: Only in Soulsilver trade.
Rayquaza: Groudon and Kyogre in party, mystery cave.
Celebi: Celebi event.
Spiky Eared Pichu: Special event.
Dialga: Need to have Arceus, then Alp ruins.
Palkia: Need to have Arceus, then Alp ruins.
Giratina: Need to have Arceus, then Alp ruins.