Everyone likes a really evil villain who gets punished at the end of the story, but I personally never found the wicked queens and stepmothers to be very convincing.
But as I learn more about royalty, I understand better why some of the wicked Queens in fairy tales behaved rather psychotic. A little jealousy is one thing, but to go to such extremes as Snow White's queen did, all the disguises and poisons, seems like too much just to hold a number one title that no one is even aware of except the mirror. But as royal people were raised, in general, they were told that they were inherently better than everyone else; that they deserved their royal position-it's a little hard for an American to understand when a presidency is fought for and held for only a relatively small amount of time. We (hopefully) respect our president but don't idolize him. But in an inherited monarchy, the Royal Family was basically one step under being God.
So their egos were totally inflated and royals were used to getting everything they wanted. Add to that the fact that royals were only allowed to marry other royals. That's really a small pool of people to choose from, and over time, royal families or local aristocratic families would intermarry several times and later generations would get a bit...unhinged.
The Countess Elizabeth Bathory (1560-1614) was quite a colorful character-she was responsible for the torture and deaths of possibly over 600 young women. I mentioned her before after reading about her in a book. The wikipedia article makes it sound like many of the things in the book stated as fact are now more exaggerated legend, but according to The Truth About Dracula by Gabriel Ronay, she believed that bathing in the blood of young virgins would make her beautiful and had girls brought to her castle claiming to give them work, where she instead found pleasure in seeing them bleed under all kinds of torture, sometimes sucking their blood or sexually abusing them. Her desire for youth and beauty drove her far beyond the extremes of Snow White's mother/stepmother, and she was only caught once she decided to move from peasants' blood to more upper class blood, because again the law was so catered to the upper class Elizabeth could get away with nearly anything-and did for quite a while.
(EDIT: Read more about the likely true story on Multicolored Diary. It's probably just as horrifying as the truth)
I learned recently of Lucrezia Borgia (1480-1519) when reading Mirror, Mirror by Gregory Maguire. He sets his novel retelling of Snow White in Italy and has her as the role of the Wicked Queen. He used some of the scandalous rumors about her-a possible incestuous relationship with her father, the Pope, and a fondness for poisons and murders make her a perfect candidate for the character. The facts about her life are not known for sure, but it makes you realize that even the exaggerated evil of the villains in fairy tales may not be all that far from the truth after all. (Technically my post title is a bit of a misnomer-it should have been "potentially real wicked queens" or something like that, but doesn't quite have the same ring to it...)