The Elder Wand is one of the three legendary Deathly Hallows mentioned in The Tale of the Three Brothers. It is thought to be the most powerful wand ever created and for several years was under used by Hogwarts Headmaster, Albus Dumbledore.
 Ancient History
One of the stories in Tales of Beedle the Bard was named The Tale of the Three Brothers. The legend told of three brothers who came across a river in which they could not cross. Using their magic, they made a bridge over the river and they proceeded to cross it. As they attempted to pass over the bridge, a cloak figure appeared before them, who was upset that the river hadn't taken their lives. The figure was Death, who tricked the three brothers into thinking that he was congratulating them and that he would give them each a gift for passing over the river. Death gave the first brother a wand made of a nearby tree and the core of a thestral tail hair as he wanted a wand that would defeat all of his enemies. One night, after killing a man with his wand, the brother, Antioch, was himself killed by man who stole the wand. The wand was taken passed through the ages, many of the owners killing the previous owner for the wand. 
 Recent History
Wandmaker Gregorovitch later possesed the wand but it was stolen by a young Gellert Grindelwald, a dark wizard. In 1945, a duel between Grindelwald and Albus Dumbledore led to Dumbledore's acquiring of the wand after defeating Grindelwald. For several years, Dumbledore used the wand to protect himself from many dark wizards including Lord Voldemort's death eaters. Dumbledore knew that the wand was in fact the Elder Wand. Dumbledore continued to use the wand until his confrontation with Draco Malfoy in the Astronomy Tower. Previously, Dumbledore arranged his death with Severus Snape to prevent a long and torturous death under Voldemort and his Death Eaters. As wand lore dictates, the power of the Elder Wand would die with Dumbledore as his death was arranged and the wand would not be "won" by Snape. However, the plan failed. Instead, Draco Malfoy disarmed Dumbledore and unbeknownst to Draco, the power of the Elder Wand passed from Dumbledore to himself; as Dumbledore died at the hands of Snape, the power of the Elder Wand lived with Draco in his Hawthorn wand.
During the events of Malfoy Manor, the power of the elder wand once again changed owners. During the rescue of Hermione Granger from Bellatrix Lestrange, Narcissa, Draco and Lucius Malfoy, Harry gained the power of the elder wand. Having been disarmed, Bellatrix Lestrange held Hermione Granger at knife point while Lucius Malfoy attempted to summon Voldemort. Dobby, the Houself, was able to cause the room's chandelier fall and nearly hit Bellatrix. In the confusion, Harry was able to take three wands from Draco: Bellatrix Lestrange's, Petet Pettigrew's and Draco Malfoy's. According to wand lore, Harry successfully "disarmed" Draco of the Elder Wand and therefore became the master of its power.