Suryavarman I (Khmer: សូរ្យវរ្ម័នទី១) usurped Udayadityavarman I, defeating his armies in approximately 1002. After a protracted war with Udayadityavarman I's son and would-be successor, Jayaviravarman, Suryavarman I finally prevailed and took sole posession of the throne in 1010.
His reign lasted some 40 years and he spent much of that time defending it. Perhaps made cautious by an eight-year long succession battle, Suryavarman I started his reign by having about two hundred civil servants pledge an oath of allegiance to him, a contract set in stone at the eastern gate of the Royal Palace.
Suryavarman I expanded his territory to the west to Lopburi, including the Menam basin in Thailand, and east into the Mekong basin. Louvo (present-day Lopburi, north of Bangkok) was a provincial capital under his reign.
Suryavarman I died in 1050 and was given the posthumous title Nirvanapada ("the king who has gone to nirvana"), a nod to his Buddhist beliefs. He was succeeded by his sons, Udayadityavarman II, who died around 1066 and Harshavarman III (Sadasivapada). The latter continued the struggle against internal rebellions and fought back assaults from the Chams until his death in 1080.