The term “Cosby Sweater” is one of the most unlikeliest legacies to come out of the #1 TV show of the 1980s.

And yet, even today, you had an image in your head of a Cosby sweater even before you saw the photo above, probably of one much similar to it.

In the first major biography of Bill Cosby written with interviews from Cos himself, author Mark Whitaker talks here about the origin story of the Cosby Sweater and how it became such a signature set-piece on NBC’s The Cosby Show. “Like a lot of things about that show, it was improvised,” Whitaker said. “It was not originally planned.” But it was all part of the design in the end.

Roll the clip!

You can pre-order “Cosby: His Life and Times,” by Mark Whitaker. The Simon & Schuster biography covering Cosby’s first 77 years is due out in September.