I ordered some of the Perry Mason show on DVD when I had a gift subscription to Netflix.
One of the discs had a lot of personal interviews and even a fairly long video of the entire cast visiting together at one of their houses. One of the more interesting things was Burr had a pretty large zoo.
Also noticed from some of the interviews that they were all, especially Hale and the guy who played Hamilton Burger, extremely intelligent. Also discovered that Barbara Hale was the Mother of the guy who played Paul Drake jr. on the later series.