How can you catch the legendary beasts in Pokemon firered?

The starter Pokemon you choose determines which legendary beast you can capture. If you choose bulbasaur, you can catch Entei, the lion Pokemon,if you choose squirtle,you can catch Raikou, the tiger Pokemon, and if you choose charmander,you can catch Suicune, the cheetah Pokemon. (You have to beat the Elite 4 and have the national pokedex)