The Pink Panther as many likely know is a creation from the 1963 film The Pink Panther which is primarily about a jewel with that name. The Pink Panther was created for promotional material, the trailer and the opening.
He first appeared in the trailer for the film, pictured above which did not have a copyright notice making it public domain. The film itself obviously isn’t but it creates the situation of the Pink Panther, the cartoon panther being public domain.
Notes
Pink Panther is a registered trademark so keep that in mind and any later appearances obviously aren’t public domain.