Hun Sen, one of the world's longest-serving prime ministers, has been in power in various coalitions since 1985.
A former communist and - briefly - a member of the Khmer Rouge - he was last reappointed by parliament in September 2013 for a further five-year term, in the face of mass demonstrations and opposition allegations of fraud in the July elections.
Since seizing power from his then co-prime minister, Prince Ranariddh, brother of the then king, Sihanouk, in 1997, critics believe Hun Sen has become increasingly authoritarian, using a mixture of electoral fraud, corruption and intimidation to maintain quasi-dictatorial rule.