Jean-Pierre Marielle
I loved his short performance. I think it's great he decided to make his character gay: never saw a gay private investigator before in a movie.
I've noticed that Argento's movies tended to be a bit ahead of their time in the treatment of homosexuals. They're heavy on the stereotypes of the age, like in mannerisms and the way they spoke, but always have dramatic importance for the movie, they're not just walking jokes.
This world is a comedy to those that think, a tragedy to those that feel.