Bluebeard (French: Barbe bleue) is the main villain of the fairy tale of the same name. He is notable for being one of the darker and more realistic fairy tale villains.
Bluebeard was a wealthy man who was named after his large beard, which was (unsurprisingly) blue, he was married many times but never seemed to keep a wife - this made him unpopular with many girls, who often refused his offers of marriage - however he managed to wed a young woman but shortly afterwards had to leave the country, he entrusted his new wife with the keys to his home but forbade her from ever entering a special room. Bluebeard's new wife grew ever more curious about what lay in this forbidden room and eventually managed to sneak a peek into the room, to her horror she discovered the room was full of the dead bodies of his many former wives - hung up on hooks (some versions say the room has severed heads of his former wives).
Terrified she locked the door again and tried to hid the fact she had ever seen the horrible room, however the key had managed to collect some blood on it which wouldn't wash away and when Bluebeard returned he spotted this, he flew into a rage and threatened to behead her on the spot - yet relented when she begged him to have time to say her final prayers.
He allowed her to confine herself to a tall tower to await her fate, however when Bluebeard - sword in hand - began to chop down the door to kill his wife her brothers arrived on the scene: Bluebeard attempted to flee but was captured and killed: Bluebeard's wealth was left to his wife, who spent it on improving the lives of her sister, brothers and finally herself - marrying a gentleman who soon helped her forget her mistreatment at the hands of Bluebeard.
The story of Bluebeard is most likely a warning against the dangers of curiosity and why sometimes it is best not to know everything.
Word Blue Beard is often used to describe violent and perverted husbands.