The Saint-Gaudens $20 Double Eagle coin was created by master sculptor Augustus Saint-Gaudens. Before the the Saint-Gaudens $20 Double Eagle coin, there was the $20 Liberty Double Eagle (which entered circulation for the first time in 1850.)
The coinage was created as a means of using up an overage in gold supply because of the 1849 California Gold Rush. They were actually never intended for general use in commerce; especially at the time of these coins being created, $20 was easily a month's wage, and it was irrational to carry one's entire month's salary all in one coin that could easily be misplaced or lost. They were instead made from the surplus of gold and used in bigger business transactions, but mainly between banks.