Kenneth A. Moskow of Concord and Chilmark died unexpectedly at the summit of Mount Kilimanjaro on Sept. 19. He was 48; the cause of death is believed to be due to altitude sickness.

Ken’s connection to the Vineyard began at a young age when his parents rented a home at Squibnocket. Later as a teenager he worked cutting fish at Poole’s Fish Market in Menemsha and learned to surf at Stonewall Beach. Surfing was a passion that stayed with him throughout his life. During his college years he worked as a carpenter for Herbert Hancock, among other things helping to build his parents’ summer home in Chilmark.

He was born Feb. 18, 1960, seven minutes before his twin brother Keith and therefore the oldest son of Michael and Donna (Melnick) Moskow. He grew up in Newton and attended the Buckingham, Browne and Nichols School in Cambridge. After high school he and his twin brother hitchhiked across the country, inspired like so many teenagers by Jack Kerouac’s On the Road. He attended Harvard University, graduating in 1983 with a bachelor’s degree in history. In college he boxed in the Golden Gloves and rowed freshman crew, competing against his twin brother who was at Dartmouth.

After college he applied and was accepted to law school, but decided not to attend, declaring that “there are enough lawyers.”

He joined the Central Intelligence Agency as an undercover operative. He became an expert on the Soviets with a focus on international terrorism, and his work took him to Spain, Cyprus, Egypt, Israel, Lebanon and Syria.

In 1990 at the age of 30 and with the end of the Cold War, he decided to leave the CIA, enrolling in the Harvard Kennedy School of Government, where he obtained his master’s degree in 1991. Following the Kennedy School he established the American Venture Corporation, doing real estate development projects in Central America as well as Boston.

He volunteered through the American Red Cross to teach English to immigrants. One evening at a restaurant he met Shelagh Lafferty, and they began dating. They eloped to Paris on Valentine’s Day 2000, four days before his 40th birthday. They had three children.

After Sept. 11, 2001, in what he acknowledged was a difficult decision, he decided to re-enlist with the CIA, moving first to Washington and then to Paris with his family.

In 2006 they returned to Boston, where he restarted his real estate development company, relishing his time closer to home with his family.

“Ken really loved people and people loved Ken,” his brother Keith said in a eulogy delivered at his memorial service. “Ken pushed himself to achieve in whatever he attempted to do. Ken loved adventures and challenges. Ken would appreciate an epitaph that says, ‘Died at the summit of Kilimanjaro.’ Unfortunately it happened 40 years too soon.”

An American flag that flew over the United States Capitol was dedicated to Mr. Moscow and sent to his three children. In an Oct. 6 letter to the children Sen. Harry Reid of Nevada, the majority leader in the United States Senate, wrote: “All those who served with your father will remember his service with gratitude. But those engaged in the gathering of intelligence know that their work must remain out of view and mind of their fellow countrymen. Hundreds of millions of Americans may never know the story of your father’s service, but we are a safer people and stronger nation for it.”

In addition to his wife and his parents, he is survived by his children, Samantha, Michaela and Jack; his twin brother Keith of Cohasset, brother Cliff of Concord, and sister Carla of Malindi, Kenya.

Funeral services were held on Sept. 26 at the Memorial Church at Harvard University.

Donations in his memory may be made to Home for Our Troops, 37 Main street, Taunton, MA 02780