Doctor Blackduck was an anthropomorphic duck.
The beloved son of the 18th century pirate Ferdinand Blackduck and his wife Mrs Blackduck, this young man disappointed his father by becoming a dentist rather than a pirate. Ferdinand was so enraged that he swore to remain on Earth as a ghost as long as it would take for one of his descendants to take up the mantle that Dr Blackduck had so frivolously discarded. For his part, Dr Blackduck apparently lived a quiet life of little interest; it is possible that he had children, but if so, none of them, nor their descendants, had yet showed an interest in piracy by the year 2000 (as by then, Ferdinand's ghost had turned to his great-great-great-grandnephew, Michael).
Behind the scenes
Doctor Blackduck was only ever (briefly) seen in 2000 story The Last of the Blackducks.
His mother's resemblance to Daisy Duck goes unexplained. It is possible she was part of one of the Duck family's lines of ancestry, which would make Doctor Blackduck a Duck relative as well.