AZD-A9S said: Huh? These two aren't rivals...like the other legendaries?
No. It's complicated, but they're like...PokeDeities. Go to www(dot)pallettribune(dot)com and look back through their radio podcast archives for their episode about all the legendaries if you're really curious.
Lugia and Ho-Oh are more like the figureheads of other legendaries. The legendary birds of Kanto (Articuno, Zapdos, Moltres) are headed by Lugia (at the least, this is seen in the second movie). The legendary beasts of Johto (Raikou, Entei, Suicune) were brought to life (or back to life, with added ability) by Ho-Oh. They're not particularly related to one another, aside from proximity.