Linda Rosenstock said she always turns to Jonathan Fielding in a pinch.

Rosenstock, the dean of the UCLA School of Public Health, said she remembers when she asked him to speak at commencement when the previously scheduled speaker was unable to make it. With less than 48 hours to prepare, he presented to the graduating class.

On Thursday, Fielding and his wife, Karin, gave the entire UCLA School of Public Health some unexpected help – a donation valued at $50 million.

The money comes in the form of the Fielding family’s stock in a private investment firm. The school can either sell the stock or receive income from it, keeping all of the revenue for itself.

“He helped out in more than a pinch this time,” Rosenstock said.

The school will be renamed the UCLA Jonathan and Karin Fielding School of Public Health in their honor. At a press conference on Thursday, in a room filled with people from the School of Public Health wearing hats with the school’s new name on the front, Rosenstock called this the “single most historic day” in the school’s history since its opening 50 years ago.

Fielding has been a faculty member at the school since 1979.

Fourteen years ago, he took up his position as the founding director of the Los Angeles County Department of Public Health. Since then he has not received a salary from the school, Rosenstock said.

Despite his busy schedule, Fielding has remained a presence on the UCLA campus. He mentors, teaches and researches for the school when he is not working for the county, Rosenstock said.

The donation will fund three areas in the School of Public Health – students, faculty and general education needs. There is a lot of freedom with the donation, Rosenstock said.

In addition, the donation will help establish an endowed chair in population health, a field that considers nontraditional factors such as transportation, education and vision when assessing public health, Rosenstock said.

Fielding said he sees his donation as an investment in the school, which has become a large part of his family’s life.

“Like all investors, we expect high return, (and that will come) when all attending students can afford to come to the school,” Fielding said. He also said he hopes the school will remain a top choice among public health leaders.

And the timing itself was right, Karin Fielding said. In 2011, the school celebrated its 50th anniversary.

“In 2012 the work begins on the next 50 years, and there is much to be done,” she said.

Rosenstock said she hopes the prestige of the award and the new position will attract a leader in population health for the endowed chair position.

Jonathan Fielding said he hopes others will follow his lead and help to support the school.

“(My family and I) love the school, and we’re committed to improving the public’s health individually and collectively,” he said.