Sure, Mad Men is about advertising, and American corporate culture, and the tidal wave of cultural change that crashed down upon us in the 1960s. But above all else, Mad Men is about human relationships, and the finest example of that is the complex, ever-evolving relationship between Don Draper and Peggy Olson.

Peggy didn’t even appear in this week’s penultimate episode (boo!), but we can’t imagine Sunday’s series finale won’t give us at least one more scene between the consummate Madison Avenue ad man and his ambitious protégé. After all, Don and Peggy’s relationship is really the heart, the soul, and the spine of the series, as they’ve progressed over a decade from boss/secretary, to mentor/mentee, to workplace rivals, to (finally) equals.

Related: The 24 Best ‘Mad Men’ Scenes, Ranked

In honor of Mad Men’s final episode, let’s take a look back at the 11 crucial moments that helped cement Don and Peggy’s relationship as one of the most fascinating we’ve ever seen on TV. (We’re gonna miss these two.)

1. Peggy is hired as Don’s secretary (Season 1, “Smoke Gets In Your Eyes”)

In Mad Men’s very first episode, a young, naïve Peggy joins the Sterling Cooper secretarial pool and introduces herself to Don as the “new girl” while waking him up from a nap (the first of many). There’s an instant rapport and mutual respect between the two; Don defends her when Pete casually lobs a few sexist remarks her way. Later, Peggy clumsily tries to seduce Don, an advance he quickly rebuffs (“I’m your boss, not your boyfriend”). But Don forgives her, encouraging her to “go home, put your curlers in… we’ll get a fresh start tomorrow.” This is the beginning of a beautiful… something.

2. Don promotes Peggy to junior copywriter (Season 1, “The Wheel”)

After impressing Freddy Rumsen during the Belle Jolie lipstick campaign, Peggy starts writing ad copy, working on women’s products like the Rejuvenator. When Pete brings in the Clearasil account, a light bulb appears over Don’s head: “We have the perfect writer for that… Peggy Olson.” Pete thinks it’s a joke, since she’s still Don’s secretary, so Don calls Peggy in and immediately promotes her to junior copywriter. Peggy is touched, and shakes Don’s hand firmly, assuring him, “I will do my sincere best.” Yes, Don’s decision is intended to get under Pete’s skin — but it’s also a vote of confidence for his eager underling.

3. Don visits Peggy in the hospital (Season 2, “The New Girl”)

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We knew Peggy had Pete’s baby at the end of Season 1, but we didn’t know exactly what happened until this episode, where Don gets into an accident with mistress Bobbie Barrett in the car and has to call Peggy to bail him out. He knows she’ll keep his secret, because he’s keeping hers: We flash back to Peggy in the hospital after giving birth, and Don is the only person to visit her. He gives her a stern speech about getting past all of this and moving forward: “It will shock you how much it never happened.” They’ve reached a deeper mutual understanding. By episode’s end, Peggy’s no longer calling him “Mr. Draper”; for the first time, she calls him Don.

4. Don approaches Peggy about jumping ship (Season 3, “Shut the Door. Have a Seat.”)

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When Don hatches a scheme to start his own agency to avoid being swallowed up by McCann (hey, it worked for a while!), he confidentially asks his star pupil Peggy to join him. But she’s tired of feeling unappreciated by him: “I don’t want to make a career of being there so you can kick me when you fail.” Don acts like he doesn’t need her, but he later goes to Peggy’s apartment, hat literally in hand, to apologize and let her know how much she means to him. He makes oblique references to their shared history, and humbly asks for her help. Peggy: “What if I say no?” Don: “I will spend the rest of my life trying to hire you.” Luckily for Don (and for us), she doesn’t say no.

5. Don and Peggy spend all night on the Samsonite pitch (Season 4, “The Suitcase”)

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This episode is absolutely pivotal, both for Mad Men and for Don and Peggy. It’s essentially a bottle episode, with the two stuck together at work hammering out a pitch for Samsonite luggage. They clash at first, with Peggy begging for a little respect and Don barking at her, “That’s what the money is for!” But they eventually spend the night brainstorming and bonding; Peggy even asks why Don never made a move on her. The next morning, Don gets the bad news that Anna Draper has died, collapsing in sobs in front of Peggy. He tells her Anna was “the only person in the world who really knew me.” But Peggy reassures him, “That’s not true.”

And check out this symmetry: Here’s a shot of Peggy putting her hand on Don’s during her awkward seduction attempt in the pilot.

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And here’s him putting his hand on hers at the end of “The Suitcase.”

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Incredible.

6. Peggy quits (Season 5, “The Other Woman”)

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Unfortunately, even the deep emotional bond Don and Peggy shared in “The Suitcase” didn’t last very long. By the end of Season 5, Don is back to taking Peggy for granted, even callously throwing money in her face when she wants to go to Paris for a client. Fed up, Peggy starts interviewing for other jobs, and later informs Don she’s accepted a position at rival Cutler Gleason and Chaough. Don thinks it’s a negotiation ploy, but Peggy’s mind is made up, even telling him, “You know this is what you would do.” Don finally accepts defeat and kisses Peggy’s hand goodbye in a tender gesture of affection. Thankfully, though, they didn’t stay apart for long…

7. Don and Peggy are reunited when the agencies merge (Season 6, “For Immediate Release”)

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Peggy positively thrived after stepping out of Don Draper’s shadow, quickly taking charge at her new firm… and even striking up an office romance with Ted Chaough. But try as she might, she couldn’t quite escape her mentor: Don and Ted conspire to merge their agencies to win the Chevy account, which means Peggy is back working under Don again — like it or not. In fact, Don’s there in Ted’s office to tell her they landed the account, and to shake her hand (again). Peggy forces a smile when the men ask her to write the press release announcing the merger, but she’s clearly not thrilled. (We were, though. More Don and Peggy!)

8. Peggy calls Don “a monster” (Season 6, “The Quality of Mercy”)

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After the merger, Peggy keeps her distance from Don, and resents being put in the middle of Don and Ted’s battle for office dominance. Plus, Don knows Peggy and Ted are fooling around, and puts a scare into them by almost spilling the beans to a client before warning Ted: “Your judgment is impaired.” A furious Peggy confronts Don, accusing him of sabotaging Ted: “You hate that he is a good man.” Don shoots back, “He’s not a good man. He’s just in love with you.” Then Peggy lowers the boom, telling Don, “You’re a monster.” She storms out, leaving Don to curl up in the fetal position. It’s safe to say this is a low point for these two.

9. Peggy is put in charge of Don (Season 7, “The Monolith”)

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Even before Don was forced to take an involuntary leave of absence from SC&P, his relationship with Peggy had frayed terribly. (See: “You’re a monster.”) When he finally returns to work, Peggy is put in charge of him, and he chafes at having to crank out taglines for his former secretary; it doesn’t help that he’s stuck in an alcoholic shame spiral. But a pep talk from Freddy Rumsen (“Do the work, Don”) puts him back on the horse, and the next morning, he’s obediently typing up taglines for Peggy.

10. Don and Peggy slow dance to “My Way” (Season 7, “The Strategy”)

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We’ve written extensively about this scene before, and with good reason: It really encapsulates the entire Don-and-Peggy relationship in a single five-minute scene. As in “The Suitcase,” Don and Peggy are working late on a difficult pitch (Burger Chef, this time), and the conversation turns intimate: Peggy confesses she doesn’t know what it feels like to be a mom, and Don confesses he’s afraid he’ll end up alone. It’s a reminder that these two know each other better than maybe anyone else knows them. They share a tender slow dance to the tune of Sinatra’s “My Way,” but of course, they don’t kiss. They know each other too well for that.

11. Peggy takes over the Burger Chef pitch (Season 7, “Waterloo”)

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This is the passing of the torch we waited seven seasons to see. With Don sensing he’s about to be fired following the death of Bert Cooper, he tells Peggy (her hair in curlers!) that she needs to present their pitch to Burger Chef instead of him. It’s her final exam, and she passes with flying colors: She uses the previous night’s moon landing to weave a stirring tale of family, community, and the power of human connection. (“There may be chaos at home… but there’s family supper at Burger Chef.”) Don’s beaming face says it all: The student has become the master. The circle is complete. Well… almost.

The series finale of Mad Men airs Sunday, May 17 at 10 p.m. on AMC.