Susan Lewis
![Sherry Stringfield as Susan Lewis](https://upload.wikimedia.org/wikipedia/en/thumb/0/0c/Susan_Lewis_Dr.jpg/150px-Susan_Lewis_Dr.jpg)
Susan appeared as a primary character in the pilot episode and left the show part way through in the third season. She later returned in the eighth season and remained as a member of the main cast until the start of the twelfth season. Finally, she returned to make a guest appearance in the series finale. Provided by Wikipedia