Lots of people will remember Alan Rickman for his roles as Snape in the Harry Potter films and as Hans Gruber in Die Hard. Neither was his greatest role, though; not exactly. His most brilliant turn was a five-minute performance as an unassuming office worker named Bill Clay.

Fans of Die Hard will get the reference instantly. “Bill Clay” is the name the villainous Hans Gruber adopts when he stumbles into John McClane (Bruce Willis) on an abandoned floor of the Nakatomi office building. (To recap: Gruber has taken over the plaza and is holding the staff hostage. Action-hero cop McClane is trying to free them.)

Gruber is evaluating some McClane-caused damage when he bumps into the man himself — and instantly shucks his villainous demeanor and his European accent. “Oooohhh, please God, no! You’re one of them!” he whines with perfect American inflection. Just like that, Rickman goes from effete ruthless villain to effete terrified victim. Good bye Hans Gruber; hello Bill Clay — a name Gruber cunningly cribs off a nearby wall office registry.

Rickman as Gruber as Clay is perfect on multiple levels. In the first place, the switch to Clay cements the central themes of the film with a mean-spirited wink. That theme being: Working-class white guys are awesome, don’t trust anyone else. The first part of Die Hard contrasts the virile, white, uncouth blue-collar cop McClane with the smooth, sophisticated Nakatomi executives—not least McClane’s own wife Holly Gennero (Bonnie Bedelia). The second part contrasts the virile, white, blue-collar cop with the sophisticated, smooth terrorist/robbers led by Gruber.

The genius of Rickman’s turn as Clay is that he fuses the film’s executives and terrorists into a single cringing thing, abject before the sincerity of John McClane’s pectorals. Rickman dials up the geek camp, chuckling nervously like he’s involved in some adolescent courtship ritual when McClane offers Clay a cigarette and babbling about his paintball exploits when McClane offers him a gun. The performance exudes a loose, brittle smarm, which echoes the sleazy entitlement of Harry Ellis (Hart Bochner), a Nakatomi executive killed off by Gruber just before this scene. The suits are all terrorists, the terrorists are all suits — and both parties are sneaky, sniveling and unmanly. Hearty cowboy McClane stands barefoot against them all, drawing a line between himself and the foreign, insufficiently hetero hordes.

But in drawing that line, Bill Clay also makes you question which side of it you want to be on. Hans Gruber is by far the most entertaining thing in Die Hard. Whether he’s oozing satisfaction while boasting about his tailor, murdering people in cold blood or falling to his death, he’s got a nonchalant wrongness that’s a lot more fun to watch than Bruce Willis’ upright hard-working authenticity. Die Hard is a conservative film: it roots for John McClane as he grapples with his working wife, Japanese execs and foreign guys who visit tailors. But Bill Clay turns that conservatism around. Suddenly it seems stodgy and dull to have to be the same muttering cowboy all day, every day, and twice on Christmas.

And then there’s Rickman’s performance. In a film that’s all about the realistic, sweating, effortful hero, Rickman casually and brilliantly embraces pretense. Clay’s self-conscious smile seems patently fake. But is it fake because Clay is a poseur, or fake because Gruber is performing as Clay, or fake because Rickman is signaling Gruber’s fakeness? Who can say?

What you can say is that Rickman is having the time of his life. And his enthusiasm is infectious. It’s a joy to watch him invent Bill Clay right before your eyes. McClane speaks with stern kindness as heroes will, but that macho swagger has nothing on the virtuoso shrug with which Rickman dons Clay’s unctuousness. Who wants to get behind boring, plain-talking Bruce Willis when instead you can cheer for the mercurial, lying aesthete — the artiste who can, with such verve, be anyone?

Rickman as Gruber as Clay neatly reverses the moral world of Die Hard. Suddenly the real dude seems like a clumsy prop, and the flamboyant mimic becomes the truth. Clay was a mask, but you wanted to see more of him — and, in a lot of ways, through Rickman’s career, you did. That nervous spark showed up again whenever he smiled. You can see echoes of it in Snape; you can see the exuberant theatricality deployed in the service of an unassuming persona in Sense and Sensibility’s Colonel Brandon.

With the news of Rickman’s passing, I repeat my thesis with a heavy heart: Clay is the moment of his stellar career, because Clay is Rickman performing performance. In acting the role of actor, he gives us five minutes of his true, false self on camera before Clay, who wasn’t there, is gone.