The Wicker Man was a large wicker statue of a human used by the ancient Druids (priests of Celtic paganism) for human sacrifice by burning it in effigy, according to Julius Caesar in his Commentarii de Bello Gallico (Commentary on the Gallic War). In modern times the figure has been adopted for festivals as part of some neopagan-themed ceremonies, notably without the human sacrifice element.
"A giant man made of wicker used in human sacrifices by druids of ancient Celtic descent. The sacrifice was held inside, then the wicker man would be set ablaze. Some tales describe the passerby stumbling across the remains wonder how they got burned. Other druid methods of human sacrifice included drowning men in barrels of water, hanging men from tress and shooting men with arrows."
Its description makes a reference to the 2006 remake of The Wicker Man, starring Nicholas Cage. There is a scene where Cage's character discovers a burned doll and demands to know "how'd it get burned?" in a over-reactionary fashion, making the scene popular for parody and remixes.