Boyhood friends of Alexandros Petersen used to tease him that he was born a century or two late, because he was at heart a gentleman explorer in the grand tradition of Lawrence of Arabia.

A scholar of Central Asia, Petersen was by all accounts living out his dream when he accepted a job teaching political science at the American University of Afghanistan. He left Washington, his home base when he wasn’t traveling the world researching energy geopolitics, for Kabul this month.

Petersen was among 21 people, including three Americans, who were killed Friday during a suicide attack attributed to the Taliban at a restaurant popular with foreigners. He was 29 and had been in the country just a week.

Friends from Georgetown Day School, where he graduated in 2003, and from think tanks where he published scholarly articles are reeling at the loss of a man who, while still in his 20s, was building an international reputation for his knowledge of lands once in the orbit of the former Soviet Union. And judging from photos he sent home of himself jubilantly astride a horse somewhere on plain in China, he was clearly having a ball doing it.

“He knew exactly what he wanted to be doing,” said Justin Parker, his best friend since elementary school and a fellow member of a punk rock band they formed in high school, the A.K.s. “Part of his dream was being out there, traveling a lot and making a difference.”

Alexandros Petersen sent home this photo of himself riding a horse in western China, on the border with Tajikistan, in April 2012. (Courtesy of Peter Silverman)

Petersen’s specialty was pipeline politics, analyzing the nexus between energy production and politics in Central Asia.

“His fundamental view was that if the countries of the Caucasus, of Central Asia, could find a way to get their energy to Western markets, it would strengthen their own sovereignty and independence, by making them less dependent on Moscow,” said Damon Wilson, executive vice president of the Atlantic Council, where Petersen was once a fellow for transatlantic energy security and associate director of the council’s Dinu Patriciu Eurasia Center.

At the Woodrow Wilson Center, where he was a scholar and an adviser on energy security issues, Petersen wrote a blog examining China’s growing influence in Central Asia. His insights stood out for his personal observations made on numerous trips to the region.

“Unlike many folks in Washington, he was not just sitting at his computer writing these things,” said Christian Ostermann, head of the Wilson Center’s Global Europe Program. “He was constantly traveling to the region talking to players on the ground. He was fantastically well-connected and knowledgeable about the issues.”

Petersen’s seriousness of purpose was evident even while he was a youth growing up in the District, the son of Effie Psalida and Christian Petersen. Both were economists, she for the International Monetary Fund and he for the World Bank. He grew up speaking Danish and Greek, the languages of his parents’ native countries, and had studied Russian and planned to learn Dari, a language spoken in Afghanistan.

“He had an intensity that’s indescribable,” said Meredith Alexander-Burke, who coached him on the high school rowing team that made it to the finals of the Stotesbury Cup Regatta, the biggest competition of its kind in the country.

He was already reading the Economist when Sue Ikenberry came to know him as a Georgetown Day School junior enrolled in her class on comparative government and politics. One day in class, he talked off the cuff for 10 minutes about Zimbabwe President Robert Mugabe.

“He was brilliant and incredibly focused,” Ikenberry said. “He was [not even] 30 years old and look at what he accomplished. Most people don’t accomplish that much in a whole lifetime.”

As a teenager, he was lead singer for the A.K.s, and his interest in geopolitics and war spilled over into the lyrics he wrote for the band. One song, called “Balance of Power,” was about Waterloo.

“I’m sure we’re the only punk band in history with a song about the Napoleonic wars,” Parker said.

In a way, the band and his academic achievements underscore Petersen’s ability to revel in two seemingly opposite worlds, his friends said.

“He loved the ad­ven­ture,” said Peter Silverman, a childhood friend who went canoeing down the Potomac with Petersen last summer. “He regaled in that romantic, adventurous notion of exploring other parts of the world and cultures.”

His friends and colleagues said he never talked to them about the risks inherent in the travel he undertook.

Ikenberry said she last saw Petersen in November, when he returned to Georgetown Day to talk to her students about Central Asia. He told her that he was heading for Afghanistan, and she expressed her concern about his safety.

“Oh, Sue,” he told her. “I’ll be fine.”