He’s developed thousands of luxury apartments and mentored countless young real estate executives, but in the years to come, J. Ronald Terwilliger’s most lasting legacy in housing may be a simple addition to a small home in a poor country.

$100 million worth of them.

This month, Habitat for Humanity announced that Terwilliger, the former CEO and current chairman of Trammell Crow Residential, had incorporated the housing nonprofit in his will, committing to a $100 million gift to support Habitat’s overseas work and affordable housing efforts.

It represents the single-largest contribution by a person in the Georgia-based organization’s history.

“We are humbled by and grateful for the unprecedented commitment Ron is making to Habitat for Humanity,” said Jonathan Reckford, Habitat’s CEO. “Thanks to his generous spirit, tens of thousands of families will enjoy greater access to simple, decent, affordable shelter worldwide.”

For Terwilliger, the massive bequest reflects the legendary real estate developer’s interest in housing and growing involvement in affordable housing issues. He recently donated $5 million to the Urban Land Institute to fund a Center for Workforce Housing and previously also gave $1 million to establish a resident fellowship for housing (currently held by John McIlwain) at ULI.

The $100 million gift to Habitat will be allocated 70% to overseas efforts and 30% to an affordable housing fund. It will help an estimated 60,000 families around the world improve their living conditions, perhaps by expanding cramped overcrowded quarters or digging a well for fresh water. According to Terwilliger, the money also represents a lead gift in a new global outreach effort that seeks to grow Habitat’s scale and scope so that the organization can serve significantly more people by 2013.

Housing is a basic need that is too often overlooked, according to Terwilliger, who joined Habitat’s board in 2000 and currently serves as its chairman. “I’ve learned that philanthropists tend to focus on education and health,” he told BUILDER Thursday, despite estimates that 1.6 billion people in the world are in need of decent housing. “Housing is not at the top of anyone’s list, except mine and a few other people’s. We think that people need to have a decent roof over their heads before they can improve their health and concentrate on their education.”

That lesson has been made real during Terwilliger’s trips for Habitat, where he has seen the group’s work in places such as Macedonia, Vietnam, Argentina, Thailand, Ireland, and more. It has been illuminating, even for someone as traveled and well-educated as Terwilliger, who graduated from the Naval Academy and Harvard Business School, where he was top of his class. “You realize how first, how fortunate you are to be an American, and two, how fortunate I have been to be a financially successful American,” said Terwilliger. “You also learn how widespread the need is.”

He told BUILDER that he hopes his gift will inspire others to examine their charitable giving.

Alison Rice is senior editor, online, at BUILDER magazine.