Smooth-talking, snobbish John D. Rockerduck got rich in the late 19th century touring the American West and tricking poor mining towns into turning over all rights to their gold to him (with promises that he would then invest in the town and "put it on the map," which he never kept, instead quickly getting away with the gold and never coming back). It was in this context that he met Scrooge McDuck, then a gold miner, and was handed his first defeat by Scrooge. Rockerduck later retired to estates of his in Duckburg.
F.O.W.L. recruited him after they found him frozen in an iceberg.