Twenty years ago today, a new TV show premiered that would last 15 seasons and spawn a lot of acting careers. It was ER, which starred an ensemble cast of not-so-well-known working actors who became household names. It also has a ton of guests stars, who played ER patients and their families and friends, or other hospital employees with minor roles. Many of those guest stars got their feet wet with the series and then got their own series or movie roles later. You know about George Clooney, Anthony Edwards, Ming-Na, Eriq La Salle, and Noah Wyle, but you may be surprised at this list of 27 other actors who started out by playing a role in ER at mental_floss.