Before the days of Grey's Anatomy and Chicago Med, there was ER, TV's longest-running medical drama. The show kept NBC viewership thriving, largely thanks to George Clooney's presence as Dr. Doug Ross. In order to keep Clooney around, NBC paid a whopping $13 million an episode for a few years. Luckily, the show later trimmed down its budget and managed to stay on air through its 15th season.