Board Thread:Super Smash Bros. Discussion/@comment-5623885-20140710145538/@comment-24229579-20140710154951

Ridley is not the main antagonist of any of Metroid games. Here's the list of actual main Metroid villians:
 * Metroid - Mother Brain.
 * Metroid II: Return of Samus - Queen Metroid.
 * Super Metroid - Mother Brain, again.
 * Other M - Queen Metroid, again.
 * Prime - Metroid Prime.
 * Prime 2 and 3 - Dark Samus.

Ridley is just an average boss, like the Koopalings in the Mario series or Gohma in the Zelda series. He is just a boss, not an antagonsit. In fact, he doesn't even appears in all of the games and most of the time, his appearance comes outta of freaking random.