Which kingdom built the temple complex of Angkor Wat?

The Khmer Empire was an empire in mainland Southeast Asia, centred on hydraulic cities in what is now northern Cambodia. Known as Kambuja by its inhabitants, it grew out of the former civilisation of Chenla and lasted from 802 to 1431 AD. Historians call this period of Cambodian history the Angkor period, after the empire's most well-known capital, Angkor. The Khmer Empire ruled or vassalised most of Mainland Southeast Asia and stretched as far north as southern China.