12 Actors You Definitely Forgot Appeared In ER

ER has featured numerous guest actors over the years, and while not everyone has gone on to be a superstar, plenty of them ended up being staples of movies and television, and you may have forgotten just how many of your favorite actors guest-starred on the series. Over 15 seasons of ER, there have been dozens of guest stars, playing patients, friends of the sick, and even doctors and nurses making a short round before they exit the show. ER wasn't one to have celebrity cameos; instead, the cameos often became celebrities.