Stanley Mandelstam, a UC Berkeley physics professor emeritus remembered for his remarkable modesty despite his sizable contribution to the field of theoretical physics, died June 23. He was 87.

Known for his contributions to quantum field theory and string theory, as well as his invention of the Mandelstam variables, Mandelstam helped usher in the “golden era of Berkeley particle physics” in the 1960s, according to Mahiko Suzuki, also a campus physics professor emeritus.

The Mandelstam variables, in particular, are perhaps the most well-known aspect of his work, according to Yasunori Nomura, the director of the Berkeley Center for Theoretical Physics. Nomura noted that every student is required to learn these variables when studying particle physics.

“He did so many things, it’s hard to pick one,” Nomura said. “He’s such a humble man, it took me some time to realize the massive amount of contributions he made.”

Mandelstam, who was born in Johannesburg, South Africa, earned his undergraduate degree from the University of Cambridge and his doctorate from Birmingham University. He started teaching at UC Berkeley in 1963 and retired in 1994.

UC Berkeley physics professors occasionally attend what Nomura described as a “tea time” — where they gather to have tea and cookies and talk about theoretical physics. During these gatherings,  Mandelstam could be seen standing in the corner and smiling — always smiling, Nomura stressed — and simply listening to people.

“He was so quiet, but when he spoke, he spoke with so much enthusiasm,” Nomura said. “I looked at him and I thought — that was a legend in the corner.”

Another campus physics professor emeritus, Mary Gaillard, remembered him for his modesty as well. She recalled an interaction with a former UC Berkeley student that for her underlined Mandelstam’s humility.

Gaillard encountered the student, who had just asked Mandelstam about his work, as he was walking out of the professor’s office. Mandelstam had revealed to the student that he was in the process of writing a proof for the fact that the superstring theory was finite.

“That was the first time I had heard about it,” Gaillard said. “That just goes to show how modest he was — it was this great scientific proof and he only talked about it when he was directly asked.”

Mandelstam was also known for having a large influence on his students, being one of the only physics professors to consistently teach undergraduate classes. Among his doctoral students is Michio Kaku, a physicist who is famous for his novels on theoretical physics and his contributions to various science documentaries.

Mandelstam is survived by his sister, Gerta Abramson, and her husband, also named Stanley. Mandelstam has two nephews named Ian and Darryl.