He first appears in the Oswald cartoon The Banker's Daughter, which is also Ortensia's debut. Sadly, this short is lost and only a poster and model sheets survive. He does appear in animated form as well in a later Oswald short. He's the old man throwing stuff at Oswald at the end of Rival Romeos. He was never named in these shorts and gained his name from the Disney Oswald comic "Just Like Magic!" (Walt Disney's Comics and Stories #726).
Appearance in modern comics
J. P. Whiskers made an surprising return in the Norwegian comic "En magisk jul!" ("Just Like Magic!"). This marks the first Oswald and Ortensia appearance in modern Disney comics outside of the Epic Mickey franchise and J. P. Whiskers' first outing in more than 70 years. Written by David Gerstein and drawn by Mark Kausler, it based on and takes place in the times of the classic Oswald shorts from 1927/1928. Even more relevant is the fact this comic was the first to confirm his name in a Disney production and re-confirm his status as a rich banker and the father of Ortensia and Homer the Cat.
In this comic, J. P. Whiskers is Ortensia's and Homer's rich banker father. He's hosting a Christmas party for the 1%; he doesn't want Oswald and his best friend Toby Bear there, but Oswald would really like to spend the evening with Ortensia and a ton of luscious food. The hungry rabbit tries to prove his good luck as a disguised Oswald and Toby sneak into J. P. Whiskers's Christmas dinner party by impersonating a man they think is the head waiter. But the "waiter" was really a hired magician, so Oswald is forced to put on a magic show with a genuine, very powerful magic hat.