Chicago Med fans may remember S. Epatha Merkerson from her days on Law & Order, but people may not know that she made her television debut as a character who worked for a different government agency.

Merkerson's first TV role was as Reba the Mail Woman on Pee-wee's Playhouse in the late 1980s. People used to be surprised by the credit, but some of its shock value has worn off by now, Merkerson tells TVGuide.com. But her Chicago Med co-star Colin Donnell begs to differ.

"It's still so good," Donnell says of the role. "Every time it comes up it's like, 'Oh my God, yeah!'"

Check out the video above to see a clip of Merkerson as Reba, and find out which celebrities have left her and Donnell starstruck.