I'm not a connoisseur or Anime so my list shouldn't be taken as such, but these were the characters I feel really added to their series. 

1. Gin - Bleach
2. Mugen - Samurai Champloo
3. Colonel Mustang - Full Metal Alchemist
4. Gennosuke Fujiki - Shigurui Death Frenzy
5. L - Death Note