And the show has a rich history. Joel originally did the show with friends Josh Weinstein and Trace Beaulieu and broadcast only on a local channel in Minnesota. I've seen parts of these episodes, and not only do the robots and sets look a lot more crude, but Joel has hair like a hippie and Dr. Forrester is missing his trademark mustache. Man, Gypsy looked freaky back then.
Then they got an actual show on Comedy Central. I believe this was a result of Joel and his "inventions" winning a stand-up comedy competition. It starred Josh Weinstein as both Tom Servo and Dr. Larry Erhardt and Trace Beaulieu as both Crow and Dr. Clayton Forrester. There weren't as many quips in the early episodes, so a lot of times you were just sitting there suffering through a horrible movie.
The following season, Josh bid farewell to the show and in came Frank Conniff and Kevin Murphy. A popular misconception made is that Frank continued the tradition of playing both one of the mads and one of the robots, but this isn't true. Frank only played Frank, and Kevin Murphy played Tom Servo. Kevin and Mike Nelson (head writer, later star of the show) also appeared during the little skits they do between movie segments as various characters.
In the episode
Mitchell, Joel gets sent back to Earth. Needing a new person to experiment on, Frank and Dr. Forrester send Mike Nelson to the Satellite of love. Mainly because Mike happened to be auditing them. The show continued with this line up for a while with guest roles played by Mary Jo Pehl.
Then some shennangins went on that I'm not sure of the details. Frank leaves and Mary Jo Pehl comes in as Dr. Forrester's mother and together they take on the task of torturing Mike. Later, there's some kind of weird time warp thing where Mike and Tom Servo are sent to the future (Crow is still around, but he didn't travel through time) and the world has been conquered by Dr. Forrester (long dead) and consequently the world is ruled by apes with Pearl Forrester as the Lawgiver. From there, people should be familiar with the show.
Interesting notes: while watching some episodes of America's Funniest Videos (the new ones, sans Bob Saget), I spied Trace Beaulieu's and Josh Weinstein's names. Listening again to some of the comments the host makes about the videos, I could tell there was some of Trace's humor in there. Also, Frank Conniff went on to be one of the head writers for Invader ZIM!
For more info, try out TV Tome
http://www.tvtome.com/
EDIT: If you haven't seen "Manos" The Hands of Fate, you haven't seen MST3K.