Silas McDuck was presumably the son of Seafoam McDuck and would become Scrooge McDuck's great-grandfather. In a futile effort to bring glory and fortune back to the name of McDuck, Silas, once head of the family, bought some land in Dismal Downs and attempted to build a new Castle McDuck to replace the ruined and haunted old one. However, his choice of location was quite poor, as it led to him incurring the wrath of a coven of druids; once more, the McDucks were ousted from their halls by a demonic hound, this time one summoned (or, as it were, faked) not by the Whiskervilles but by the Druids.
Earning himself the name of Potcrack, the dishonored McDuck, after moving to Glasgow, invented a steam-powered bagpipe in 1767, which he called the Steam-o-Pipe. The machine's cacophonic music was not to the tastes of the time, and Potcrack never found a buyer; however, his neighbor James Watt actually copied Potcrack's Steam-o-Pipe when inventing his own steam engine. Potcrack later married with an unknown woman and had several children, including Titus McDuck, who would become Scrooge McDuck's grandfather.
At some point afterwards, Potcrack heard that gold had been found in the brand new United States of America. He decided to move there and become a prospector, and his nickname shifted to Potluck. Although he dug a large mine, he never found any gold, and instead used his mine as a storage facility for all sorts of old junk he collected. His heir and great-grandson Scrooge McDuck eventually inherited the mine, where he actually found Spanish doubloons hidden amongst the junk.
Behind the scenesEditScrooge McDuck's great-grandfather McDuck first appeared as such in January of 1974 in the story Old Potluck's Payoff (never yet published in English) drawn by Tony Strobl, under the name of Potluck McDuck. The character was then used in 1992 by Don Rosa in The History of Clan McDuck, where he was instead called Potcrack McDuck.
In Johannes A. Grote's Duck Family Tree, a portrait of an old duck seen on Donald Duck's wall in Carl Barks's Going Ape (1948) is identified as Scrooge's great-grandfather, father of Titus McDuck. As the duck does indeed resemble Potcrack as drawn by Don Rosa, there is no reason not to consider this to be canon.