Duck Amuck, the greatest cartoon short of all time (says me):

Wikipedia:

According to director Chuck Jones, this film demonstrated for the first time that animation can create characters with a recognizable personality, independent of their appearance, milieu, or voice. Although in the end, the animator is revealed to be Daffy’s friend and rival Bugs Bunny (who famously declares “Ain’t I a stinker?”), according to Jones the ending is just for comedic value: Jones (the director) is speaking to the audience directly, asking “Who is Daffy Duck anyway? Would you recognize him if I did this to him? What if he didn’t live in the woods? Didn’t live anywhere? What if he had no voice? No face? What if he wasn’t even a duck anymore?” In all cases, it is obvious that Daffy is still Daffy; not all cartoon characters can claim such distinctive personality.