Editor's Note: The following contains minor spoilers for Season 19 of Grey's Anatomy

When Addison (Kate Walsh) first strolled into Seattle Grace Hospital right before the credits rolled on the Grey's Anatomy Season 1 finale, there was no telling what kind of ride audiences were in for. She introduced herself as “Addison Shepherd,” AKA Derek’s (Patrick Dempsey) estranged wife, and seemed to spell nothing but trouble. However, there was no way of knowing just how much of an impact she would go on to have on the show. She was more than a roadblock for Derek and Meredith’s (Ellen Pompeo) relationship, and she was definitely more than just Derek’s wife. She held her own and was a strong, capable character that was so layered. She may have left Grey's Anatomy as a series regular in the show’s third season but even with every new character that has come and gone, Addison’s mark on the show has remained strong, and without her, it wouldn’t be what it is today.

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Addison Is the Meryl Streep of Maternal-Fetal Medicine on 'Grey's Anatomy'

Kate Walsh, played by Addison Montgomery, driving on 'Grey's Anatomy.'
Image via ABC

Addison’s joining of the Seattle Grace crew took a bit of convincing. She and Derek were on the outs (he called her Satan!) ,and she had a whole life back in New York. But Richard Webber (James Pickens Jr.) was determined to keep her around, and he got his way, even if she did primarily agree to stay in an attempt to save her marriage with Derek. Her becoming a regular would spell drama for both Meredith and Derek, but while that may have been her original role, she quickly proved that there was much more to her than just the ring on her finger that made her Mrs. Shepherd.

Not only was Addison a phenomenal doctor (and one of the foremost neonatal surgeons in the country) but she also had a lot of heart to her that just brought so much to her character. She fought hard for her marriage, even when it felt hopeless, even when she knew Derek had eyes for Meredith. She cared immensely for her patients and did everything she could for them. And she was an incredible mentor to those around her, most notably Alex Karev (Justin Chambers.) Without her, Alex likely would have stayed his cold, grumpy, pompous self with little remorse for those around him. She forced him onto her service as punishment, but he actually grew to respect it, and thanks to her found a real appreciation and interest in neonatal surgery. Her time as a main character in Grey's Anatomy may have been brief, but she left an impact.

This is why she scored her own spin-off, Private Practice, in which she relocated to L.A and took a job offer from her friend Naomi (Audra McDonald) to join her practice. One of Shonda Rhimes' best TV shows and a worthy spin-off, Private Practice peeled back even more of Addison’s layers and allowed viewers to know her on an even deeper level, learning that she was much more fragile and damaged than she ever let on. Her arc was beautiful as she grew into herself and put together her missing pieces. She went on to run the practice and also became a mother to Henry through adoption after struggling with fertility issues. Her fertility issues were one of the biggest and most poignant pieces of the show and her character, and we watched as she continuously struggled through the difficulties of IVF, adoption, and everything in between before it eventually worked out for her. This arc went on to become one of the most poignant storylines and resonated with so many viewers of the show, giving it a major leg up in terms of storytelling.

But there was another storyline that was pivotal, and that was Amelia’s (Caterina Scorsone) battle with addiction. Amelia had consistently been described as the most reckless of the Shepherd siblings, dating back to when she witnessed her father’s murder as a child. Despite being clean for a while, she unfortunately relapsed during Private Practice’s run after joining the practice and becoming a part of the surgical route there. The team of doctors rallied around her and staged an intervention for her, with Addison at the front lines of it, still seeing Amelia as a little sister despite her divorce from Derek. It’s a tough-to-watch stretch of episodes, but seeing Amelia come out on top of it was all worth it, and the friendship she and Addison built remains one of the sweetest in the show.

Addison Left an Important Mark on 'Grey's Anatomy'

Meredith, played by Ellen Pompeo, and Addison, played by Kate Walsh, during Season 18 of 'Grey's Anatomy.'
Image via ABC

In Greys Anatomy’s most recent seasons, it has been tackling more real-world issues, such as covid-19 and most recently abortion bans. It's the latter of the two which has Addison making more frequent guest appearances on the show. Before Season 18, her most recent appearance was all the way back in Season 8’s musical episode, meaning it had been about 10 years since Addison had last visited — and yet it felt like she had never left.

She first made her comeback at Grey Sloan in Season 18, coming up with a research project on uterine transplants. It was during it that we finally saw her reaction to Derek’s death, as well as when she met him and Meredith’s children. It was a relatively lowkey arc for her, but it showed that her prowess for her career hadn’t faltered, and it also let her vulnerable side shine through again as she revealed how hard the pandemic had been on her.

In the current season, Grey's Anatomy is continuing its foray into real-world issues and has given Addison a heroic arc as she works on the front lines and fights for the right to choose. She reveals that she’s been threatened, stalked, and doxxed as she’s set out to help women seek proper and healthy abortion care. She never gives up and that’s perhaps one of the most alluring parts of her character. She’s resilient and she’s a fighter, and she will stand up for herself and her patients.

Her impact and legacy are long-standing among the halls of Grey-Sloan Memorial, even if she only pops in sporadically, and there’s something to be said for that. Even over 15 years after her final appearance as a main character, she’s just as prominent as ever, and will forever remain one of Grey's Anatomy’s most valuable players.

Episode 16, "Gunpowder and Lead," of Season 19 of Grey’s Anatomy airs this Thursday, April 20, on ABC. Check out the promo below: