Thurston, Knots to Narnia 

There are three RU-vid videos in this series:
Thurston, Knots to Narnia
Thurston, Knots to Narnia in class, part 1
Thurston, Knots to Narnia in class, part 2.
William Thurston (1946-2012) recorded them with me at UC Berkeley on March 4 and 5, 1992.
Bill explains how the trefoil knot can be interpreted as generating a six-fold cover of three-space. His son Dylan is quoted in the New York Times obituary as saying that "Math was always very fun for him." Here we can glimpse how much fun it was for those who knew him.
The first day is edited from several takes; the second day is an unedited 16 minutes of his class, split into 2 parts for RU-vid.
Tony Phillips