Costumes and Costumers of the 1960s
UPDATED! Costuming and Cosplay are not a recent thing. Convention costuming really started at the first Worldcon in 1939 (NYcon 1), when Myrtle ("Morojo") Douglas dressed herself and her then-boyfriend Forrest ("Forry") J. Ackerman in costumes inspired by pulp magazine covers:
But costuming really took off at conventions in the 1960s, paving the path to become the huge international convention and costuming/cosplay community that it is today.