Palace Maven Spenser is the 5th Frontier Brain of the Hoenn region. He lives in the wild and he knows how to make Pokémon medicine and food with the help of his Venusaur.
In the Manga
He was accused of being the person that was behind of all troubles by Ruby and Sapphire because he also touched the Blue Orb, but it was later revealed that he wasn't. Also, when Emerald lost to Tucker, Emerald changed his plans and battled Spenser.
Spenser's Battle Sprite
Venusaur is Spenser's main Pokémon, although Scott has mentioned that it's less powerful than Claydol. Spenser often rides on Venusaur.