42 famous people you forgot were guest stars on 'Grey's Anatomy'

You don't get through 13 seasons without casting some stars.

By Mahalia Chang

Even though a lot of the Grey's Anatomy cast are in it for the long haul — averaging between 100 to 300 episodes, depending on their level of commitment — a large majority of the characters are one-or-two episode guest stars.

And considering this show has churned through 13 seasons in more than 12 years, it's safe to say that some of those guest stars were pretty well-known.

Book an OR, this one's gonna be a ride.