Stephen Furst (born Stephen Fuerstein on 8 May 1955 in Norfolk, Virginia) is an American actor, best known for his roles as "Flounder" in the feature film Animal House (1978), as Gonzer in the feature film Up the Creek (1984), as Dr. Elliot Axelrod in the television series St. Elsewhere (1983-1988), and as Vir Cotto in the science fiction television series Babylon 5 (1993-1998).

In 1972, Furst's father died from diabetic complications and Furst was diagnosed with diabetes. One of his sisters has also been diagnosed diabetic and is now blind, confined to a wheelchair and dependent on oxygen. After almost having to have his left foot amputated due to diabetes complications in 1996, Furst lost nearly 150 pounds (68 kg) in the time between the third and fourth seasons of Babylon 5. When filming started for the fourth season, the show's producers found that all of the costumes were now too large for Furst. His weight loss is easily visible in the later seasons of Babylon 5. This weight loss had not been explained within the context of the Vir Cotto character. He wrote the book Confessions of a Couch Potato about his weight loss and diabetes, and co-wrote and directed a video called Diabetes For Guys, an attempt to educate about good diabetic control through humor.

Although not a regular, he also appeared in the short-lived 1992 TV series The Amazing Live Sea Monkeys.

In the 1995 animated TV series Freakazoid, he voiced the character Fanboy.

In 2001, he directed the low-budget movie Title to Murder starring Christopher Atkins and Maureen McCormick.

In 2002, he guest starred in an episode of Scrubs.

Stephen directed two low-budget movies for the Sci-Fi Channel, Dragon Storm in 2004 and Path of Destruction in 2005.