Basic premise
"As many intelligent people know, aliens are all around us. This is a story of a band of four such explorers. In order to blend in, they have assumed human form. This is the High Commander [Dick]. He has assembled an elite team of experts: A decorated military officer [Sally], a seasoned intelligence specialist [Tommy] and, well, they had an extra seat [Harry]."
Cast
3rd Rock maintained a constant ensemble cast, the four main characters – Dick, Sally, Tommy, Harry – with the exception of Tommy, all appearing on the show for every episode of the six seasons it ran. Several other main characters who left or joined the show through its original run supplemented these four, and numerous guest stars and one-time characters supplemented all of them.