KEO is a Kyrati corporation in Far Cry 4 specializes in mining and Gold. It seems to be the only major business in Kyrat's existence.
While KEO's employees and exact history are unknown. They where implied to be founded in the 1800s when the British Empire colonised Kyrat after the country got it's independence from The British Empire presumably after The Second World War due to the amount of weapons styled from that time period, KEO was allowed to stay and soon Kyrat's economy became dependent on the company, Gold and mining.
During the 60s, KEO's mines began to dry up and exhaust causing KEO to lose funds and soon the mines where completely exhausted causing KEO to go bankrupt and Kyrat's Economy went into freefall that would lead into chaos and civil unrest in the 70s and eventually into civil war.
The Royal Army now occupies the mines in Kyrat now under the dictator Pagan Min, while the mines where thought to be exhausted they're maybe still Gold inside of them and where probably used for Pagan Min's Gold statue.