A timeline of the most important things to happen to ER
September 19, 1994
Season 1 begins, and will go on to win eight Emmys, including Juliana Margulies' for best supporting actress.
September 26, 1996
Jeanie Boulet (Gloria Reuben) learns she has HIV; many other regulars will face their own health crises.
May 14, 1998
ER gets its biggest audience ever — 47.8 million viewers — when it follows the Seinfeld finale.
February 18, 1999
George Clooney leaves the show, but will return for a surprise cameo in 2000 for Margulies' ER swan song.
September 30, 1999
Goran Visnjic joins the cast, eventually becoming the show's new romantic center with Maura Tierney.
November 16, 2000
Sally Field plays Tierney's mom, and wins an Emmy. Future Emmy bait: Ray Liotta and Don Cheadle.
May 9, 2002
Succumbing to a brain tumor, Dr. Greene (Anthony Edwards) is one of six hospital staffers to die thus far.
September 25, 2003
Season 10 begins: Parminder Nagra, Scott Grimes, and Linda Cardellini will join the crowded ER.
May 19, 2005
Last original cast member Noah Wyle leaves. Counting return cameos, he appeared in the most episodes: 254.
November 10, 2005
John Stamos joins the show, picking up the "hunky doctor" mantle once carried by Clooney and Visnjic.
April 2, 2009
After past castmembers returned to pay respects, the series ended on episode 332.