“Excelsior” has long been Lee’s catchphrase. In the mid-1960s, not long after Atlas Comics rebranded as Marvel, Lee wrote a monthly column for the comics publisher in which he’d sign off with “Excelsior!”—a Latin word meaning “ever upward.” He told io9 in 2007 that he wanted a unique word to himself that his rivals at the time wouldn’t be tempted to copy:

I used to have a lot of expressions that I would end my comic book columns with: Hang Loose, Face Front, ‘Nuff Said, and I found that the competition was always imitating them and using them. So, I said I’m going to get one expression that they’re not going to know what it means, and they won’t know how to spell it. And that’s where excelsior came from, and they never did take up on it, thank goodness.

But what started as a clever sign-off to thwart his competition in the 1960s quickly became an optimistic mantra the writer would exhibit throughout his life and career for many decades after. Or maybe it was part of him all along.

Lee, a singular figure in American entertainment who was responsible for much of the Marvel superhero universe we know today, has demonstrated the meaning of “Excelsior!” throughout his life. He was renowned for his relentless imagination (he created or co-created hundreds of fully fleshed characters), pioneering spirit, and a heroic work ethic. The writer had worked well into his 90s, and in the last decade alone, he started an imprint for kids, published a graphic novel, and was reportedly writing a superhero rock opera. And, of course, he was always game for a cameo appearance in the Marvel movies based on his creations.

He was also famous for being available—and excited—to talk with fans at conventions and other comic book events. You’ll likely notice many tributes in the next few days recognizing Lee’s unyielding positive energy, a trait that by all accounts was just as constant in his later years as it was when he was an upstart writer for Captain America in 1940.

For Lee, “excelsior” wasn’t just a term to remember him by. It was his nature—creating, striving, ever upward.

📬 Sign up for the Daily Brief

Our free, fast, and fun briefing on the global economy, delivered every weekday morning.