Blackheart Beagle is the grandfather and founder of The Beagle Boys.
He first appeared with his sons in "The Fantastic Riverboat Race" in Uncle Scrooge Goes To Disneyland. His next appearance was in "The Money Well" in Uncle Scrooge 21. Of course he was only referred to as Grandpa Beagle in that story. It was later established by Don Rosa that Blackheart and Grandpa Beagle are the same character.
In The Life and Times of Scrooge McDuck Part 2, Scrooge first encounters Blackheart and sons while working for his Uncle Pothole. In Part 10 Scrooge and his sisters encounter Blackheart and his sons at Fort Duckburg shortly after they move into the city. In Part 12 Scrooge encounters Blackheart again but this time his sons are replaced by his grandsons who are the Modern Beagle Boys. Blackheart has returned in A Little Something Special to lead the alliance between Scrooge's most primary adversaries who include The Beagle Boys, Flintheart Glomgold, and Magica De Spell. He makes one final appearance in The Beagle Boys Vs The Money Bin where He stays in jail throughout the entire stories while his grandsons try to rob Scrooge's Money Bin. Blackheart also appeared in the Vicar Story Dime and Dime Again where he and The Beagle Boys steal Scrooge's Number One Dime and it gives them bad luck as opposed to the good luck it gives Scrooge. It is revealed in this story that Blackheart's Real Name is Humboldt.