cakravartin (Sanskrit). A ‘Wheel-turner’, a monarch or emperor whose rule is unbounded as symbolized by the free movement of the wheels of his chariot throughout the land. Four grades of cakravartins are distinguished, the wheels of their chariots being iron, copper, silver, and gold respectively. The term was also used as an epithet for the Buddha whose teachings also pervaded all lands. The cakravartin represents the Buddhist political ideal of the just ruler or universal monarch who brings peace and prosperity to his subjects, and various kings in history have been seen as embodying this ideal, notably Aśoka. Representing political authority, the cakravartin may be thought of as the secular counterpart of a Buddha, and both are said to bear the 32 marks (dvātriṃśadvara-lakṣaṇa) of the superman (mahāpuruṣa) on their bodies.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)