Wally
The character Wally, who you meet early on in the game, can be thought of as a rival since he pops up a few times in the story and can be refought after you beat the Pokemon League. You first meet him in Petalburg City as he prepares to travel to Verdanturf Town, wanting a Pokemon to keep him company. Your father Norman tasks you with helping him catch a Ralts in the grass outside the city.