Like Grandma Duck, Grandpa made his first appearance on a picture in the Donald Duck newspaper comic strip drawn by Al Taliaferro. Here, he was seen wearing an American Civil War soldier's uniform, implying that he served in the army at some point during the Civil War.
In the 1964 comic The Good Old Daze (Donald Duck #93), illustrated by Tony Strobl, one of the most beloved duck masters of all-time, Grandpa Duck appears in flashback taking care of little Donald along with Grandma on their farm. He's portrayed as a dedicated but rigorous grandfather. Donald remembers him as being lazy, making his own grandson do the work on the farm while "helping" with eating Grandma's pies himself.
Grandpa's real name was not mentioned in this comic. However, in a 1967 story called The Giant of Duckburg (Donald Duck #111), also illustrated by Tony Strobl, Donald's late grandfather Daniel Duck (alias Grandaddy Daniel) appears in a flashback.
Previously, in an untitled story (Vacation Parade #2, 1951), Grandma recalls memories of an old lover of hers named Humperdink. In this same story, Grandma remembers an occasion where she and Humperdink heard one of her favorite songs. She says to herself, "I remember the band played that for Humperdink and me at the Fish Peddler's Picnic...in 1905!". Besides, Grandma finds the ruined coat Humperdink had used to prevent her from stepping on a mud puddle and some romantic letters addressed to her that were written by Humperdink.In another comic published that same year (Walt Disney's Comics and Stories #129), Grandma is pressured into dressing up by her new maid and she picks a dress that reminds her of time spent with Humperdink. On the Duck Family Tree printed in Walt Disney's Comics and Stories #300 (1993), Humperdink and Grandpa Duck were included as the same character, thus implying that Humperdink became her husband.
On Giovan Battista Carpi's 1990s Duck family tree, Strobl's Grandpa Duck and the Grandpa Duck from the cartoon were included as different characters, the first as Donald's actual grandfather and the latter as Donald's great-grandfather. The original cartoon did, however, not make any mention of this.
Humperdink Duck had relevant comic appearances in flashback sequences in two stories by Don Rosa: The Invader of Fort Duckburg (chapter 10 of the comic series The Life and Times of Scrooge McDuck) and The Sign of the Triple Distelfink.
In a comic story first published in 2013, Grandpa Duck appears in a flashback scene which is told by his wife Grandma Duck. This story is called The Good Neighbors and is written by Lars Jensen and drawn by Flemming Andersen and makes part of the comic sub-series Tamers of Nonhuman Threats.