Duckworth was the butler and housekeeper of Scrooge McDuck. He was extremely loyal to Scrooge, and his favorite butler; he was known to throw the best parties, and was the one Scrooge always entrusted with planning out his birthday party. Duckworth died at an unknown point before 2017, and Scrooge stopped celebrating his birthday, convinced that no one else could throw a party as good, and because he secretly missed Duckworth.
In 2017, when Huey Duck decided to throw Scrooge a party anyway, he hired an illusionist, Nik Nokturne, to entertain the guests. Nokturne was actually a Beagle Boy intent on causing mayhem, who attempted to summon a demon from the Beyond to crash the party. Being rather inept at sorcery, he ended up summoning the ghost of Duckworth, who, taking advantage of the situation, pretended to be a demonic monster in order to chase away Nokturne and other villains who had infiltrated the party.
Following these events, Duckworth was introduced to Huey, Dewey, Louie and the rest of the new inhabitants of McDuck Manor, and he resumed service as Scrooge's butler (which caused a few problems with Scrooge's housekeeper Bentina Beakley, who had gotten used to running the house by herself).
As a ghost, Duckworth is capable of phasing, disappearing, and shapeshifting into a skull-faced demonic version of himself.
Behind the scenes
This version of Duckworth first appeared, disguised, in the opening credits of DuckTales 2017, starting with Woo-oo!. His true nature (and true form) were only revealed in McMystery at McDuck McManor.