Who created the Statue of Liberty and why?

The Statue of Liberty is a monument commemorating the centennial of the signing of the United States Declaration of Independence, given to the United States by the people of France to represent the friendship between the two countries established during the American Revolution.

Frédéric Auguste Bartholdi sculpted the statue and obtained a U.S. patent for its structure. Maurice Koechlin, chief engineer of Gustave Eiffel's engineering company and designer of the Eiffel Tower, engineered the internal structure. The pedestal was designed by architect Richard Morris Hunt. Eugène Viollet-le-Duc was responsible for the choice of copper in the statue's construction, and for the adoption of the repousse technique, where a malleable metal is hammered on the reverse side.

(Answer taken from Wikipedia.)