John Arrillaga Sr., a land developer and philanthropist, passed away Monday morning at the age of 84. The billionaire, whose name was not known by many outside of Bay Area circles, is credited for helping to develop the modern-day Silicon Valley. As founding partner of real estate giant Peery Arrillaga, he converted the area’s fruit orchards into valuable commercial space back in the 1960s.

According to an obituary published on Medium by his daughter, Laura Arrillaga-Andreessen, Arrillaga and his firm built corporate campuses totaling more than 20 million square feet. Over the decades, these included the office complexes of companies like Intel, Google, and more. Arrillaga also played a key role in the development of Sand Hill Road, the hub for venture capitalists in nearby Menlo Park. His son-in-law happens to be co-founder of famed VC firm Andreessen Horowitz, Marc Andreessen. (Andreessen tweeted about his father-in-law’s passing Monday evening.)

Arrillaga was also known for his philanthropy: His name is etched on buildings throughout the Bay Area, particularly on the campus of Palo Alto’s Stanford University, where he once donated $151 million, the largest single gift from an individual the campus has ever received.

According to his daughter’s post, Arrillaga “went to the Stanford campus almost every single day of his adult life, where he was renowned for walking the campus and personally picking up every single piece of trash he saw and rearranging single stones in fountains across the campus.”

In the weeks before he passed away, Arrillaga had offered to donate more than $30 million to Palo Alto, part of an initiative to help the city build a new public gym. But in addition to being a prolific donor, Arrillaga was famous for being hands on with his philanthropic projects. (His daughter says picked every palm tree planted at Stanford University’s new football stadium, which he funded.) He had told the city of Palo Alto he would give the money if he could help pick the design and the contractor for the development. It’s not clear what will happen to the project now that Arrillaga has passed away, but the real estate billionaire leaves behind not just his fortune and the buildings that bear his name, but also a legacy: According to his daughter, Arrillaga worked seven days a week at the age of 84, “literally negotiating leases until the day prior to his passing.”