Dead ringer is an American expression dating from the late 19th century meaning an exact duplicate. 'Dead' here is used simply as an intensifier to add emphasis, as in phrases like 'dead right', 'dead centre' etc. The expression derives originally from horseracing, where a ringer (in the early 19th century) was a very fast horse substituted as a lookalike for a very slow one in order to defraud bookmakers. Ringer now means anyone trying to play down his or her skills for gain. Ringer in the foregoing senses derives from the very much older use and meaning of ring (c. 1611) as in something having a false or genuine 'ring' to it. Stories of dead ringers being seemingly dead people buried alive with life-saving bells, is pure folkloric myth.