Story artist Bill Peet boarded all of "101 Dalmatians" by himself.
He had definite ideas about the construction and flow of the story, but Bill also had strong opinions for what the characters should look like on the screen.
Ever since "Song of the South" (which Peet also boarded) it had been established that Milt Kahl would take a look at Bill Peet's story drawings, and from there he would polish the look of the characters for animation.
Most often this process worked swimmingly. Peet provided the overall concept, and Kahl refined it with outstanding design and draughtsmanship.
Yet when it came to finding the final design for Pongo both artist found themselves butting heads.
Milt had finished a few drawings showing Pongo next to Perdita, but Bill Peet was not impressed. "Pongo's muzzle is too large, that doesn't look like a Dalmatian, that's a Great Dane" he argued. I am sure Milt responded with a few angry choice words, defending Pongo's muzzle size to better contrast Perdita's.
In the end though Milt gave in and adjusted his design.
I wonder if Walt himself helped to settle the matter.
Bill Peet Milt Kahl
One of my favorite scenes with Pongo shows the final design.