While it appears that this information is ripped from the Castlevania wiki, they got it from Wikipedia before the Walter & Joachim articles were removed. And who wrote those articles? I did, in September 2005! (With help from Marfisa's translations, of course!)
name: Walter Bernhard
age: physically 42; true age unknown
location: the forest known as Eternal Night
voice (Japanese): Kishino Yukimasa
voice (English): Jamieson Price
weakness: cross, holy water
attacks: beat down, hellfire, dark inferno, shadow inferno, mana flare, demonic megido
Translated by Marfisa. ♥
perfect guide description
A vampire of unknown age who settled in the bordering forest, but no one is sure since when. His demonic power is enormous and he has the power to make it eternally night in the forest under his control by means of the Ebony Stone. He is a dangerous hedonist who enjoys thrilling games because he has eternal life, but his manner is stubbornly refined.
He met Mathias when he decided to enjoy a life risking game as usual. On Mathias' advice, he kidnapped Sara, dragging Leon onto the game's stage. But even Walter didn't realize he was being used as part of Mathias' plan until the end, and his soul was stolen.
official guide description
Walter is a dark king who rules over Eternal Night. Even among the vampire clan, he is the strongest. He cannot even be scratched by inferior weapons.
The vampire who controls the forest called Eternal Night. His origin and his age are not clear. To distract himself from the boredom of eternal life, he enjoys playing life and death games with brave humans. To raise the stakes of the game, and in order to catch the human's interest, he steals that which is most precious from his target.