I have enjoyed a number of movies starring Walter Matthau, and admired him for the wide variety of roles he played, while as far as I know not playing himself (as many actors do). While he sometimes played Jewish characters -- including Albert Einstein -- his repertoire wasn't limited by his ethnicity. My favorite of his films is "Hopscotch."
As far as I know, he was in fact religiously observant, and outspoken against antisemites like Vanessa Redgrave when she denigrated Israel. I find him admirable.