At first, his firefighter colleagues were wary when Roy W. Chelsen, the physically imposing leader of Engine Company 28, told them to run for it. One of the twin towers was gone, and they were in the one still standing. Mr. Chelsen remembered saying, “Let’s just get these people, and let’s get out of here.’’

Persuasion gave way to command, and his colleagues in the lobby of 1 World Trade Center fell in behind him, running beside a brick wall outside toward a pedestrian bridge over West Street.

“We got out and we got under the bridge,’’ Mr. Chelsen told a commander in January 2002, during an interview for an oral history of Sept. 11, 2001. “A couple of bodies came down, flying down, just in front of our guys. We just got under the bridge and, like: ‘OK, it’s safe. It’s good.’ All of a sudden, we heard this huge explosion, and that’s when the tower started coming down. We all started running.’’

It is a story that was not well known while he was alive, mostly because he was not one to talk about it, said Stephen J. Cassidy, head of the Uniformed Firefighters Association.

“This is one of those classic, unbelievably tough New York City firefighters,’’ Cassidy said. “He did not say a lot, but when you needed him, he was there.’’

Cassidy added, “There are a lot of firefighters alive today because of him.’’

Now, in the days since Mr. Chelsen’s death on Sunday at age 51, at his home in Warwick, N.Y., his colleagues and others are retelling the stories of their lost friend, who spent his career in the firehouse on the Lower East Side. They remember a big, plainspoken firefighter with a cleft chin who rode a Harley-Davidson motorcycle and moved through burning buildings with athletic grace.

“He was a very, very strong man,’’ said Kevin Murray, 36, a firefighter who followed Mr. Chelsen to safety. “He looks like he is a Viking. It usually takes two guys to hold a hose line, but he could hold it himself. We called everything Roy did ‘Roy’s world,’ because he just had a way of getting things done.’’

It was ironic, Murray said, when Mr. Chelsen died in his living room on Sunday evening, at 5:45, and “the date was 1/9/11 — which is just like Roy to do something like that.’’ Firefighters, family, and friends were there when he drew his last breath, Murray said, bantering and “busting each other’s chops,’’ the way their pal would have wanted it.

“He took the firefighters and their fraternity, or brotherhood, to heart,’’ said Mr. Chelsen’s son, Christopher, 24. “To say he loved it is an understatement.’’

Mr. Chelsen, 51, first got sick about five years ago. He died after a five-year battle with multiple myeloma, a cancer that the New York Fire Department, his relatives, and others consider linked to his service on 9/11 and his work in the ensuing weeks searching the rubble for lost colleagues. When he retired in December 2006 (he joined the force in April 1985), he received a World Trade Center disability pension, officials said.