Christopher W. Walker, 66, a Washington area commercial real estate developer who climbed many of the world’s tallest mountains, including Africa’s Mount Kilimanjaro, and once paddled a kayak through the Grand Canyon, died Aug. 31 at his home in Middleburg.

He had multiple myeloma, said his wife, Helen H. Walker.

Mr. Walker began working in the commercial real estate industry in the Washington area in the early 1980s. He built an office building near Dupont Circle before becoming one of the first developers to start commercial projects in Reston.

In all, Mr. Walker’s 13 multimillion-dollar developments spanned more than 1 million square feet, according to his company’s records.

Mr. Walker helped found the Dulles Corridor Users Group, a nonprofit organization that seeks to make the Dulles toll road free to use.

In the late 2000s, Mr. Walker filed a lawsuit on behalf of his nonprofit group against the Metropolitan Washington Airports Authority, in which he alleged that the Dulles Toll Road violated Virginia law. He said the MWAA, which owns and operates the toll road, owed real estate owners as much as $200 million in toll money.

Mr. Walker said that the toll road hurt business owners and was a “cash cow” being used to help pay for the Metro extension to Dulles International Airport. In 2010, a U.S. District Court judge dismissed the case.

Christopher Wetmore Walker was born in McCook, Neb., and grew up in Bethesda.

After graduating from St. Albans School in Washington, he received a bachelor’s degree in psychology from Yale University in 1966. He graduated from Harvard Law School in 1969 and received a master’s degree in business from Harvard in 1971.

An inveterate tinkerer, Mr. Walker designed his own exercise machine and helped found a computerized dating service in college.

As a child, he harbored a fascination with astronomy and gazed at stars through a telescope. As an adult, he became an opponent of light pollution and was a board member of the International Dark-Sky Association, which helps communities address problems with outdoor lighting to reduce glare and make the night sky more easily visible.

An outdoorsman, Mr. Walker scaled many peaks in North and South America as well as the Matterhorn in Switzerland.

Survivors include his wife of 40 years, Helen Heisserer Walker of Middleburg; two children, Ellen Walker of Paris and Evan Walker of Amsterdam; and two brothers, Jonathan Walker of Chevy Chase and Peter Walker of Sebastopol, Calif.

— T. Rees Shapiro