While the doctors and nurses at County General Hospital are known for their romantic entanglements, the friendships on ER are the show's true backbone. These medical professionals are in the trenches with each other every single day, and it's impossible for people to work that closely together without forming strong bonds. While some of the series' BFF pairs are downright iconic — the bromance between Carter and Benton is the stuff of legend — others are woefully underrated. However, if there's one ER friendship that definitely deserves way more love, it's the one that exists between nurse Carol Hathaway and Dr. Mark Greene.
It's easy to assume that the only connection between Mark and Carol is their love for Doug. As the fan-favorite pediatrician's best friend and one true love, respectively, there's no way for Mark and Carol to avoid being in the same orbit. But here's the thing: their friendship isn't based on Doug. They have a real connection with one another that forms the foundation of a captivating platonic relationship.
Remember, Carol is always the first person to call Mark out when he lets the stress of the job to make him lose sight of why he became a doctor. In Season 4, when Mark says they can't help people who won't help themselves, Carol shoots back, "No, Mark. Those are exactly the people we should be helping." Throughout her time on the series, she consistently keeps Mark grounded and focused on doing what's best for every patient, no matter how frustrating they could be.
There's nothing one-sided about their relationship, though. Mark provides Carol with emotional support after her suicide attempt and during her on-again/off-again relationship with Doug. And when she becomes pregnant with twins, Mark is the one who tells her she's having two babies, instead of one. Perhaps the most poignant moment in their relationship comes when Mark is by Carol's side when she gives birth. Her delivery is a difficult one, but Mark's jokes and encouragement help Carol get through it. She even names one of her daughters Kate in honor of Mark's mother. Even when Doug isn't part of the picture, these friends have each other's backs.
At every turn, Carol and Mark challenge each other and tease one another, but when times are tough, they also stand by each other. While their friendship isn't as prominent as the one that exists between Mark and Doug, it still provides ER with some of its funniest and most emotional moments. Carol and Mark are ER's truest unsung BFFs, and these two long-time pals deserve to have their friendship remembered.