There are countless versions on how a margarita was invented and the most popular versions are as follows :
-- In 1948 a socialite called Margaret Sames was hosting a party at her cliff side house in Acapulco, Mexico. Among her guests was Conrad 'Nicky' Hilton of the famous hotel family (the one Paris belongs to). Looking for something to pep up the party, Margaret began to experiment at the bar and created the first Margarita.
-- Pancho Morles, a bartender from Juarez, Mexico was asked to make a magnolia but could not remember the exact ingredients so threw something together. Although it wasn't what the lady asked for but she loved it - her name was Margarita