In 1915, Stonehenge was bought at auction by a man named Cecil Chubb. As the legend goes, Chubb was only there to buy a set of dining chairs. Instead, he acted on impulse and made the winning bid for Stonehenge.
Prior to its purchase, the monument was in a perilous condition. A popular attraction since the Middle Ages, by the 19th century people were known to chip the stones for souvenirs and scratch their names on the monument. In 1881, timber was used to prop up stones considered to be in danger of collapse while in December 1900, an upright sarsen stone fell and the massive horizontal lintel it held in place snapped in two.
Chubb’s impulsive purchase marked a turning point in the care and protection of the ancient monument. Three years after purchasing it, Cecil Chubb donated it to the nation to secure its future. A major survey and programme of restoration followed. Today, English Heritage proudly continues to care for Stonehenge so that generations to come can be inspired and delighted by one of the world's most important prehistoric sites.
EDIT: Quite a few people have asked how much Chubb paid for Stonehenge and who owned it before, so here's the answer...
Stonehenge had been owned by the Antrobus family since the early 1800s but when the heir to the Antrobus baronetcy was killed in the opening months of the First World War, the estate was divided into lots and put up for sale via auction. And so at 2pm on 21 September 1915, the Palace Theatre in Salisbury was “filled with an interested audience, intending purchasers and spectators” and in the hands of Messrs Knight, Franck and Rutley, Stonehenge went under the hammer.
“Surely someone will bid me £5,000 to start with,” urged the auctioneer, Sir Howard Frank. A hand in the stalls was held up, and in calm, business-like tones it was announced that the first £5,000 bid had been received. Bidding increased by £100 increments from £6,000 until the figure of £6,500 was reached by local man Isaac Crook, whose grandson Richard still farms the fields around Stonehenge today. One more bid was received, “the hammer remained aloft for an instant; there was no further offer and it descended with a sharp rap.” Stonehenge was sold for £6,600 to Cecil Chubb.