The champion is Pokemon Diamond, Pearl and Platinum, is Cynthia. She has various Pokemon-types. She is the Sinnoh Champion. Her Pokemon are Spiritomb, Lucario, Togekiss, Milotic, Garchomp and Roserade. In Platinum, Cynthia has a Togekiss. In Diamond and Pearl, she has a Gastrodon.
You find Cynthia in a villa in Undella Town across from the Pokemon Center. For the first time battling her,she asks you your name. Later, she'll appear in Spring/Summer for DAILY battles. Her Pokemon are at the same level.