Akira Kurosawa’s Yojimbo might be said to include a depiction of a character with Down Syndrome: Inokichi, the brother of Ushitora the gangster. Inokichi is portrayed as overweight with a unibrow, possibly to imitate the physical characteristics of the syndrome. He’s the object of derision from many of the other characters, and generally expected to carry out the dirty work his brother orders him to. Inokichi certainly does not display the empathy most people with Down Syndrome are known for, but he’s shown to be subjected to physical violence on a regular basis if he does not make a display of toughness.
The character of Kannuki the Giant is treated slightly better, since his size (and the giant wooden mallet he wields) intimidate many.