Beatrice is the main character or, if you want, antagonist of the series. She appears with her human appearance just at the end of the first game, The Legend of the Golden Witch, when she talks with Battler, who can't believe in her no matter what.
She says of herself that she's fickle, and she loves to drink tea and to eat sweets, she especially likes ice-creams. Her personality is very simple to understand: since she's the Golden Witch, with the power of killing endlessy and resurrect whoever she wants, she's very dreaded from the other of her kind, and she's considered the most powerful witch among all.
Because of her eternal life, she's often bored and in search of something that can enjoy her: the thing that will lead her to continue her game with the Ushiromiya family, will be the determination of Battler to won't accept her existance. She has a lot of servants, and it is said that she has 72 demons who are her furnitures and work for her.
She's definitely not very polite, she likes to laugh all loud, I can say she's a very spontaneous person, who loves to trick the others, especially if she find them amusing. She has no pity of anyone, she just wants to enjoy herself and to find interesting ways to spend her equal days.
Beato is really a liar, so... don't believe to everything she says. :D