On March 14, 2018, renowned astrophysicist Stephen Hawking, known for his many scientific works, passed away peacefully at his Cambridge home at the age of 76.

Hawking defied the odds, surviving more than 50 years longer than doctors predicted after he was diagnosed with amyotrophic lateral sclerosis (ALS), also known as motor neurone disease or Lou Gehrig’s disease. He was eventually left paralyzed and unable to speak, relying on a speech-generating device to communicate.

Among the millions mourning the loss of such a brilliant mind are the cast of “The Big Bang Theory,” a show on which he appeared a number of times and showcased his awesome sense of humor.

On one 2012 episode, he asks to meet Sheldon because of a paper he wrote. Little did Sheldon know that Hawking did so to tell him his thesis was wrong because of an arithmetic mistake. Watch the clip below:

After his death, the cast shared a behind-the-scenes photo from his appearance with the caption, “In loving memory of Stephen Hawking. It was an honor to have him on The #BigBangTheory. Thank you for inspiring us and the world.”

In loving memory of Stephen Hawking. It was an honor to have him on The #BigBangTheory. Thank you for inspiring us and the world. pic.twitter.com/9rWoYqIToy

— The Big Bang Theory (@bigbangtheory) March 14, 2018

Mayim Bialik, who plays Sheldon’s fiancée Amy Farrah Fowler, payed tribute as well in her own post. “As we near Pi day (3.14) I join the global community in mourning the loss of the greatest physicist of our era. #StephenHawking is free from the physical constraints of this earthly condition we all exist in and he is soaring above us now marveling at it all.”

As we near Pi day (3.14) I join the global community in mourning the loss of the greatest physicist of our era. #StephenHawking is free from the physical constraints of this earthly condition we all exist in and he is soaring above us now marveling at it all. pic.twitter.com/o3V0TZrppj

— Mayim Bialik (@missmayim) March 14, 2018