After the event, Mr. Paulson strolled out of the park with Mr. Blonsky, and the two discussed how the gift had come about.

Mr. Paulson had been a supporter of the conservancy for years, and he and Mr. Blonsky had taken walks together in the park, but he had never given the group a large gift. In the spring, they began talking about the donation seriously, but the details were not made final until the day before the announcement.

The gift is the latest in a year in which city parks emerged as major beneficiaries of philanthropy, joining more traditional recipients like museums, hospitals and universities. A year ago, the Diller-von Furstenberg Family Foundation pledged $20 million to the High Line, the elevated park on the West Side of Manhattan; that donation followed two other gifts to the High Line from the foundation, totaling $15 million. In April, Joshua P. Rechnitz, an amateur track cyclist, announced a gift of $40 million to Brooklyn Bridge Park to build a field house with a cycling track.

Half of the $100 million donation to Central Park will go toward its $144 million endowment, which helps finance maintenance, while the other half will pay for capital improvements. In his remarks, Mr. Paulson, who runs and rides his bicycle in the park, singled out two projects in particular: restoration of the North Woods, with its waterfalls and scenic paths, and landscaping improvements around Merchant’s Gate in the park’s southwest corner, its busiest entrance.

Nothing in the park will bear Mr. Paulson’s name, which is unusual for a gift of this size.

Mr. Paulson, born and raised in Queens, described his family’s long connection to Central Park: his grandparents had their first date there in the 1920s, his mother was pushed in a baby carriage there, and, later, she took him there in his own carriage as a youngster. He recalled the scruffy 1970s and early ’80s, when the park was in “serious disrepair — its infrastructure was crumbling, its landscape was in shambles and it was plagued with drugs and crime.”

In recent decades, he has watched firsthand the transformation of the park, which has received an infusion of $700 million over 33 years, allowing for top-to-bottom restorations. Most of that was raised privately by the conservancy from residents, corporations and foundations.

Asked what prompted the gift, he said: “Walking through the park in different seasons, it kept coming back that, in my mind, Central Park is the most deserving of all of New York’s cultural institutions. And I wanted the amount to make a difference. The park is very large, and its endowment is relatively small.”