Della Thelma Duck (nicknamed Dumbella) is one of Walt Disney's comic book characters. She was the daughter of Hortense McDuck and Quackmore Duck. According to comics writer Don Rosa, Della was "born" in 1920. Her twin brother is Donald Duck; she is also the mother of Huey, Dewey and Louie Duck.

Her husband's identity is something of a mystery, as he is hidden by a bird and several branches on Disney comics artist Don Rosa's family tree. While Rosa revealed that Della's husband is the brother of Daisy Duck, little else is known about him. It was revealed in an early comic that Mr. Duck was sent to the hospital because Huey, Dewey and Louie placed a firecracker under his armchair as a prank, with disastrous results. It was because of this incident that Della (or "Dumbella" as she was called in the theatrical cartoon that introduced the nephews) sent her sons to her brother, Donald Duck. While originally meant to be a one-month stay, the nephews wound up staying with Donald permanently; the reasons for this are unknown.

In one Donald adventure, Donald Duck dresses up in a long, red wig and notes how much he looks like his sister. Several stories written by Rosa also show Della as a child, alongside her brother Donald.