Original: At the Spear Pillar, Cyrus uses the Red Chain to bring the legendary Pokémon Dialga (in Diamond) or Palkia (in Pearl) out, planning to use their power to distort spacetime and so create the new universe, over which he will be the new deity (or so he thinks).
Simplified: At the Spear Pillar, Cyrus uses the Red Chain to bring the legendary Pokémon Dialga (in Diamond) or Palkia (in Pearl) out, planning to use their power to create the new universe, over which he will be the new leader.