Caviar - or the roe of a sturgeon - has been consumed since Egyptian times, but it was in the mid-15th century that Rabelais mentioned it in "Pantagruel" as the finest item for what would eventually become known as the Hors d'oeuvres. It was introduced to France in 1920s following the exile of Russian princes the Petrossian Brothers, and soon began appearing on the menus of restaurants and Western European.
98% of the world's caviar comes from the Caspian Sea, where the Russians, and in lesser part the Iranians, harvest thousands of tons each year.
When using caviar, it's recommended that one open a chilled tin a few minutes before serving, foregoing garnishes like lemon, capers, or chopped onions for that of thin toast, blinis, unsalted butter, or sour cream. Other classic accompaniments include separately-chopped hard boiled egg, iced vodka and Champagne. It is classically served in small crystal bowls or directly from the tin, on ice, with an ivory or mother-of-pearl spoon.
References:
Oxford Companion to Food; 1999; Page 148
Larousse Gastronomique; 2001; Pages 234 - 235
Food Lover's Companion; 2001; Page 108
Joy of Cooking; 1997; Pages 174 - 175