In all the pokémon games, there has been a rival or two who is not a playable character and who is sometimes a friend of the player and sometimes a douche a more aggressive rival. Except for the Hoenn games, so I chose to count Wally as a rival there but you can do as you wish. In the manga, he even gets the Sceptile from Professor Birch.
Which is your favorite rival overall? What is your favorite incarnation of that rival character? Most of them appear in the Pokémon Special manga and some of them appear in the anime (Silver has a little cameo buut).