An individual is considered a billionaire if their wealth reaches or exceeds one billion units in a major currency like the U.S. dollar, euro, or British pound, translating to a thousand million in that currency. This classification falls under the broader category of ultra high-net-worth individuals. Forbes, a prominent American business magazine, annually compiles and continually updates online a worldwide roster of individuals who have amassed wealth exceeding one billion U.S. dollars. John D. Rockefeller, an American oil tycoon, earned the distinction of being the first verified billionaire in U.S. dollars in the year 1916.