The character was created in 1981 to host a weekend B-horror movie show Elvira's Movie Macabre. Elvira was played by Cassandra Peterson, and quickly gained notoriety for her witty commentary and revealing appearance.
Apart from the TV show, Elvira appeared in a number of movies and spawned a whole line of Elvira-themed merchandise. A number of computer games featuring the character were created - they include Elvira: Mistress of the Dark, Elvira II: The Jaws of Cerberus and Elvira: the Arcade Game.
More information on Elvira can be found on Cassandra Peterson Wikipedia Entry.