The phrase "dead ringer" comes from Old Medieval England when someone was pronounced dead they were quickly sent for burial due to no refrigeration in mortuaries. This led to some wrong diagnosis and the burial of people who were actually still alive. Many a resumed coffin has been found with server scatch marks on the inside. A contributor of this was the fact that beer, when drunk in large quantities from the old "lead beer mugs" made the thirsty person not only drunk but the appearance of being dead due to the fact the the chemical reaction between the beer and lead slowed the heart beat of the said thirsty person to such an extent that an over enthusiastic dockter may pronounce the drunkard, dead. However, if they were not buried so swiftly they would in fact wake up with no more than a regular and deserved "hangover". Once this was realized and before there was a ban on drinking out of the early beer mugs made of lead, people were buried with a bell so that they could ring it if they were to wake up while 6 feet under. This is also where "saved by the bell" comes from.
During a race or any gaming activity where a particular "unknown" participant excels, they can be termed a "dead ringer", in other words they are back from the dead.