Third Rock from the Sun (aka 3rd Rock) focuses on the antics of an expeditionary group of aliens beings posing as a 'human family' in the fictional town of Rutherford in the state of Ohio. Their observations of human society and how they interact with the humans they encounter drives the comedy.
As the series progresses other aliens are introduced, including some in recurring roles played by big name Guest Stars.
The Humans who inhabit Rutherford Ohio are completely unaware of the aliens in their midsts, even as they work, play, fight, become romantically entangled with them. They do sense that they are not normal, but only in an unsettling sense. They never suspect that the real reason could be something out of this world. This is largely explained by the fact that humans, by nature, either are too self-absorbed, or else they get too caught up in other people's problems, to ever really notice what is going on around them.
The character of Dr Mary Albright (played by Jane Curtin) becomes a central figure on account of her professional and personal relationship with Dick.
Other series regulars include Nina Campbell (Simbi Khali), Dick and Mary's secretary; Mrs Dubcek (Elmarie Wendel), who rents out her loft apartment to the Solomons; the students of Pendleton University where Dick finds a job as physics professor.
The character of Officer Don Orville (Wayne Knight) was initially introduced as a recurring character but emerges as series regular as his relationship with Sally intensifies.
Other characters had recurring roles in the series.