A very young Robin Williams. I was going to say bizarre, but he is already that.
In the second season, the theme was modified to a more disco arrangement—an attempt to attract younger viewers. Disco, nice.
I found a bunch of public releases for the theme song—all of them in vinyl!
So I guess that’s it, nothing much left to say here. Below is the original opening sequence from the first season. After that comes the second season modified disco theme.