Philanthropist GREGORY C. CARR has spent more than a decade giving away his money to humanitarian causes. The former owner of Prodigy has also backed cultural endeavors in Harvard Square.

He’s got one foot in Cambridge, a second in Idaho and a third in Afghanistan.

This seemingly multi-footed entrepreneur-turned-philanthropist is Gregory C. Carr, one of Harvard Square’s most quietly influential people.

As he walks around Harvard Square at a brisk clip that would exhaust any normal person, he points out the various projects and buildings he’s backed over the last decade, from the center that bears his name at the Kennedy School of Government (KSG) to the empty parking lot at Zero Arrow St. that will soon be transformed into a 320-seat theater.

Since he graduated from KSG in 1986, he’s turned giving money away into a full-time career.

“This world is just so chock full of fabulous ideas,” he explains.

Carr says he just wanted to play a role in turning such ideas into reality, and so began the rapidly spreading empire of Carr’s benevolence.

He has a small whiteboard in his apartment on which he keeps track of what his Carr Foundation is doing around the world.

On the left, he’s scribbled a bunch of numbers and financial calculations; on the right, there’s a running list of projects he’s involved.

In Cambridge, Carr is building an elaborate theater and has donated the money to fund the Kennedy School’s Carr Center for Human Rights; in Idaho, in addition to purchasing the old Aryan Nations headquarters and donating it to a university, he’s given a natural history museum and a memorial to Anne Frank; and—as his latest challenge—he’s creating a radio station in Kandahar, Afghanistan.

And Carr is just getting started.

Broadway in Cambridge

On the desk in his office above Wordsworth on Brattle Street, Carr has piles of blueprints for his new Market Theater—a state-of-the-art complex to be located in the parking lot at the intersection of Mass. Ave. and Arrow Street.

The first iteration of the Market Theater, which opened in fall 2001 in Winthrop Square above Grendell’s Den, was considered the best thing in years to hit the Cambridge theater scene, which some say desperately lacks performing arts venues.

But that location lasted less than a year. Last May, Carr announced that he was leasing the space to a restaurant, Upstairs on the Square—formerly Upstairs at the Pudding—which will reopen this fall.

According to Carr, the rent Upstairs on the Square pays on the old Market space will go to the Carr Foundation’s philanthropic efforts.