The Khmer Empire began in 802 with Jayavarman II, who declared himself a God-King. The Khmer Empire flourished until the 15th century. It was during this time that the Angkor complex was built. At its peak, the Khmer Empire covered much of modern day Cambodia, Thailand, Laos and Vietnam. This civilization was constantly at war with those around them in order to defend their territories.
The Khmer Empire was full of great builders. They are primarily known for the magical temple called Angkor Wat, but they had huge stone buildings and a large transportation network that included bridges and a highway extending 800km. All said, it is estimated that Angkor covered 1,150 square miles and was the capital of the Khmer Empire. It was the largest pre-industrialized city in the world. The buildings, like Angkor Wat (Wat means temple in Khmer) were built by various kings of the Khmer Empire.
Until the 13th century, when monks brought Buddhism to the area, Hinduism was the main religion of the empire. A shift then took place and it can be seen in many of the temples where the Hindu carvings are defaced or modified to Buddhist carvings.
Angkor Archeological Complex is a UNESO World Heritage Site, but ticket sales and the profit from these sales (thought to be around $60 million dollars last year) all go to a private company called Sokimex. Very little of the money actually goes to restoration of the temples. Several ruins were found in the early 2000s and are still overrun by trees and vegetation. That money comes from foreign countries.
No statistics are published, but it is likely that Sokimex shares these profits with the government and the already incredibly wealthy politicians. In the year 2017, the Cambodian government will take back control of ticket sales, citing corruption as the main reason.