His cry of "Danger, Will Robinson, danger!" became an all-purpose phrase for every kind of "don't go there" situation. Although I never hear it today, another casualty of the passage of time. Over 40 years since that series began.
That robot, BTW, was originally created for the 1956 sci-fi classic Forbidden Planet
. He was "Robbie the Robot" there, and was so successful he was recycled for a few other movies, and many TV shows.
For Lost in Space they modified him extensively, keeping only the basic torso. He got a new head, and legs that were locked together over tractor treads, whereas formerly he could walk on 2 feet. I believe a second robot was eventually built for the series, as well.
This site doesn't allow links to pics, but click on "All About Robby" to read his history and see some photos:http://www.the-robotman.com/