The King Kong Commentary
The genesis of the now ubiquitous commentary track (on DVD and BluRay releases) can be traced back to a 1984 Criterion release. In the 1980s they put out a Laserdisc of the 1933 classic King Kong that had the first ever commentary. Apparently, this audio commentary by Ronald Haver began with the film historian explaining what exactly such a film commentary was.
Here’s an excerpt from that now famous commentary. Among other interesting tidbits, it reveals an unexpected connection between King Kong and… condoms.