Eric Schmidt, who led Google for well over a decade as CEO and then executive chairman, could easily have retired in 2020 at age 65. But he’s stayed active as an author, CEO, and startup founder, most recently launching Bolt Data & Energy to develop power and data center campuses in West Texas.

“Meaningful work keeps you engaged and energized,” Schmidt, now 70, told Fortune in an emailed interview. “Henry Kissinger was my best friend and mentor, and he worked every day well past the age of 100.

“He believed that periods of major change demand responsibility and action, not detachment,” Schmidt said of Kissinger. “That perspective shapes how I approach AI today, making sure we stay actively involved in guiding its impact for public good.”

It’s no coincidence that Schmidt and Kissinger, the famed former U.S. secretary of state and longtime corporate adviser who died in 2023, coauthored the 2021 book The Age of AI: And Our Human Future, publishing it a full year before the launch of ChatGPT.

Schmidt and Kissinger met early on during Schmidt’s Google CEO tenure. Schmidt invited Kissinger to the headquarters, where Kissinger promptly told Google employees the company was “a threat to the world’s civilization.” They became fast friends from there, and Schmidt helped Kissinger adopt new technology, including his first iPad and his first selfie.