When he returned in the spring to visit Belmont Hill School, First Lieutenant Charles Kenney was a slightly older version of the student he had once been, and just as charismatic.

In his broad smile all could still see the award-winning public speaker, and the hockey player who was at his best facing the imposing odds of an ­opposing team’s power play.

“He looked great,” said Rick Melvoin, the school’s headmaster. “By then we already knew he was going to Afghanistan. Everyone was incredibly proud of him, but wanted to make sure he stayed safe over there. Charlie just smiled and said, ‘Don’t worry.’ ”

On Aug. 20, Mr. Kenney was two weeks from being deployed with his ground intelligence unit from the Seventh Marine Regiment when he died after suffering a seizure while visiting his girlfriend, Charlotte Rizzi, and her family in Bethesda, Md. He was 25 and had grown up in Jamaica Plain.

“Charlie was a bold, confident, and strong-willed kid,” Dave Antonelli, a close friend from their days at Belmont Hill, said during a eulogy Friday in St. Ignatius Church on the Boston College campus, where hundreds filled every available space in the sanctuary to celebrate Mr. Kenney’s life.

“Everyone gravitated ­toward him,” Antonelli said. “He had an effortlessness about him; no one commanded more respect and attention. In many ways, this captivating personality is what I would later recognize in him as outstanding leadership.”

Those leadership skills also were much on display at Brown University, where Mr. Kenney was captain of the lacrosse team, and in the Marines.

“I loved working for Charlie,” said Marine Sergeant James Newman, who met Mr. Kenney in January. “His leadership was honestly second to none. I can’t think of a better leader, and I’ve served for six years.”

Though he was an officer, Mr. Kenney often sought input from those he led.

“A lot of guys would let their pride get in the way of the job,” said Newman, who worked with Mr. Kenney on numerous training exercises. “If he didn’t know something, he would ask for help.”

That approach would not have surprised those who knew the younger version of the officer Mr. Kenney became.

“In practice, when we were working on different skills, he would always work on his weaknesses to make sure he was getting better,” said Ken Martin, who coached Mr. Kenney on Belmont Hill’s varsity hockey team. “A lot of guys just work on the things they’re good at.”

The Marines, of course, asked more of Mr. Kenney than what was demanded in athletic competitions at a prep school or an Ivy League university.

“I trusted Charlie with my life, just like I know he trusted me with his,” Newman said. “I definitely would have followed him anywhere. I know for a fact that if push came to shove, Charlie had my back.”

Born in Boston, Charles F. Kenney was the son of Anne Detmer and Charles C. Kenney.

“He always had a great story to tell,” Martin said of Mr. ­Kenney. “A lot of the people in his family had served their country, either in the fire department or in the service. Charlie would always talk about people serving and helping others.”

Descended from firefighters who responded to the Cocoanut Grove nightclub fire in 1942 and who served on an elite rescue crew, Mr. Kenney drew on family heritage for a speech that brought him a public speaking prize at Belmont Hill when he eloquently talked about how his paternal grandfather joined the Navy at 17.

Alert listeners might have heard in that speech a foreshadowing of decisions Mr. Kenney would soon make.

“Charlie Kenney had the advantage of knowing what he wanted, to be a professional soldier,” Mr. Kenney’s godfather, Tom Vallely, who directs the Vietnam program at the Harvard Kennedy School’s Ash Center, said in a eulogy. For someone who went to Belmont Hill and majored in international development at Brown, Vallely added, “it was an unusual choice.”

As a Marine officer bound for deployment, Vallely said, Mr. Kenney “wanted to experience reality as it presented itself. Whether there was going to be mission victory or failure was not the main issue for him. He wanted to go to Afghanistan to learn, to lead, and to understand.”

In choosing that path, Mr. Kenney headed toward a familiar role.

“He was always the grinder battling for a puck in the corner while someone else scored the goal,” said his father, a former Globe reporter and editor. “He loved that role. Others had more talent, but he always wanted to be the best teammate, the leader.”

Mr. Kenney’s mother said he “was first and foremost a natural leader. That was clear in sports, in the Marine Corps, and in every aspect of Charlie’s life.”

Family was perhaps the most significant part of his life. Clear to all was his devotion to his younger sister, Elizabeth, who is studying in New York City at Parsons The New School for Design, and his parents.

And Bob Rizzi, the father of Mr. Kenney’s girlfriend, Charlotte, said in a eulogy that “it was easy to see how happy Charlie and Charlotte were together, as if they were able to relax and let go of the other worries and concerns in their lives and just enjoy each other.”

In addition to his parents, sister, and girlfriend, Mr. Kenney leaves his paternal grandfather, Charles Jr. of Harwich, and a step-grandmother, Josephine Detmer of Cumberland Foreside, Maine.

In his eulogy, Antonelli quoted a friend who once said: “Charlie, simply put, was great at living.”

Although Mr. Kenney could “flip the switch from fun to business unlike anyone else,” Antonelli added, “I’m pleased to stand before you and confidently say that the switch was more often than not turned to fun.”

The example Mr. Kenney set, Antonelli said, “will guide all of us through the rest of our lives.”

“I know that I’ve lost him,” said Martin, Mr. Kenney’s former coach, “but he’s still there every day, you know? The memories of Charlie will always be there.”