The Sunday Irving Schachter died, he’d planned to run 18 miles in Central Park, his third and longest run of the week. At 75, the former physics professor was in training for his second New York Marathon.

“I didn’t think of him as elderly,” his wife, Hindy, told The New York Post shortly after he died. “He was a fantastic amateur cyclist. We liked to go to the theater, we hiked.”

The couple met in the summer of 1967 and married shortly after. They settled on the Upper East Side and Irving got a job teaching AP Physics at Brooklyn Technical High School in Fort Greene, where he taught for decades and was known to his students as “Shack”. “He was a brilliant guy,” said former student Eugene Cheleshkin told The Post. “He could take a complicated subject and make it fun.”

His son-in-law, Alexander Levi, told the Post that Schachter enjoyed applying his knowledge of his physics to his passion for cycling. “He would have entertained all your debates about the physics of collisions, momentum, mass, acceleration, and demystified it all for you, with a broad smile,” Levi said.