Sir Quackly McDuck is one of Walt Disney's comic book characters, created by Carl Barks.

Sir Quackly was a descendant of Sir Eider McDuck, born in Scotland in the year 1010. He later became the leader of The Clan McDuck. In 1054 King Macbeth I of Scotland offered him a small treasure chest in exchange for his support in the ongoing war for the throne. Sir Quackly agreed and served the king during the war. He became obsessed with protecting the treasure, so he created a secret crypt in the walls of his armory in order to keep the chest safe. In 1057, Dismail Downs, the clan's main castle, was under siege by men controlled by Malcolm Canmore, later Malcolm III of Scotland. Sir Quackly decided to check on his crypt, but when he entered, Sir Quackly had a stroke of bad luck and the door locked behind him, trapping him inside the walls of his armory where he subsequently died. Soon King Macbeth was also dead, so the clan served Malcolm.

Sir Quackly's descedants include Sir Stuft McDuck. Sir Quackly became a legend among the McDucks who claimed that his ghost protected the treasure and the castle. Sir Quackly's remains, his armor and the treasure chest were found by his descendant Scrooge McDuck in 1948.