When cranky secretary Ida Blankenship died in Mad Men's season four Bert Cooper memorialized her by saying: "She was born in 1898 in a barn. She died on the thirty-seventh floor of a skyscraper. She’s an astronaut." In the show's midseason finale, Cooper dies watching men walk on the moon.

Cooper wasn't necessarily a good man—his objection to seating Dawn at reception because she's black being a distasteful recent example of his more insidious qualities—but he was one of Mad Men's true originals, and one with a mischievous spirit. He was, as he tells Roger in last night's episode, always a leader, which means he could embrace his oddball tendencies: his interest in Japan, his hatred of shoes. His eccentricities at times obscured a shrewd and ruthless mind for the business, and, if we're going to be honest about it, the show regarded him as a secondary character, deploying only when necessary. 

Cooper's send off—a post-death song and dance number visible only to Don—is as much of a tribute to the character as it is to his portrayer. Casting Robert Morse was the show's great inside joke, since Morse is an icon of the Mad Men era for having played How to Succeed in Business Without Really Trying's J. Pierrepont Finch both on stage and screen. The episode's conclusion is both a grace note to a longstanding character and something of a wink to the audience who knows Morse's musical theater history. 

While the rest of the agency is upstairs memorializing Cooper, Don goes downstairs to work, where he imagines Cooper as a song-and-dance man. Cooper sings "The Best Things in Life Are Free," crooning its lyrics "the moon belongs to everyone/The best things in life are free" as secretaries dance backup. But that's not something Cooper always believed. This is the man that bought a Rothko thinking about how its value would increase; the man who told Don to read Ayn Rand when giving him a $2,500 bonus. Cooper was ruthless, and Roger knew that. Does Don? Just before his death, Cooper doesn't even have faith in Don. "No man has ever come back from leave, even Napoleon," he tells Roger. 

Cooper's death inspires Roger to take charge of matters at the company, becoming the leader Cooper said he wasn't earlier in the episode, and wresting control of the company away from Cutler and his vision. Roger gets the rest of the partners, including Cutler, on board with a plan that would see the agency becoming a subsidiary of McCann Erickson. The partners get a financial boon out of the deal, and Roger maintains control and Cooper's legacy. 

But in death, it's not Cooper's head for business that Don idealizes but rather his impish spirit. Don sees the man who romanticized Ida Blankenship. He sees an astronaut. For this episode at least, Don rejects cynicism. He chides Sally when she says that the moon landing is a "waste of money." He puts his faith wholeheartedly in Peggy. He isn't even bitter when he splits up with Megan. He sees Bert dancing off into death singing a song that is essentially about finding love. But his reaction to Bert's soft-shoe-with-no-shoes is one of sadness, almost hopelessness, and you can't help but think of the worries Don enumerated to Peggy in the penultimate episode of the season. His concerns? "That I never did anything and I don't have anyone."