By Raisa Bruner
November 12, 2018

On Monday, the world learned of the passing of Stan Lee, the 95-year-old co-creator of many of Marvel Comics‘s most beloved franchises, including Spider-Man, the X-Men and the Incredible Hulk.

Lee was remembered by a chorus of fans online, who thanked him for his legacy — of humanizing superheroes, creating indelible characters and, in the words of comedian Seth Rogen, “making people who feel different realize they are special.” Ryan Reynolds, Mark Hamill, Robert Downey Jr., Jamie Lee Curtis, Elon Musk and more paid tribute to Lee and his contributions to pop culture.

One common phrase popping up in tributes to Lee is the term “Excelsior.” Even CNN’s Jake Tapper used the word “excelsior” in his Tweet honoring the late creative, while Iron Man‘s Robert Downey Jr. hashtagged it in his post.

What does it mean when Stan Lee said Excelsior?

“Excelsior” was Lee’s catchphrase, which he used to close out his comic book columns. He once explained to an interviewer that it was “one expression that they’re not going to know what it means, and they won’t know how to spell it,” since he didn’t want it to get copied by his competition. “And that’s where excelsior came from, and they never did take up on it, thank goodness,” he added.

Of course, it is being taken up now as a way to remember the late, great icon.

Besides his work as a writer and publisher for Marvel, Lee was also known for his memorable cameos in Marvel movies, where he would pop up to play a side character, becoming a cult favorite in front of the camera as well. “They say you should never meet a childhood idol. They are wrong,” Star Wars‘s Hamill wrote, calling Lee “revolutionary.”

Read celebrity reactions to the death of Stan Lee below:

Write to Raisa Bruner at raisa.bruner@time.com.

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