The American essayist, poet and philosopher Henry David Thoreau once wrote: “The hero is commonly the simplest and obscurest of men.”

 Two brave young men who faced remarkably similar horrors in different parts of our country, and reacted in the same manner, may fit this bill.

 Riley Howell, 21, was an ROTC cadet at the University of North Carolina-Charlotte. In late April, he was attending an anthropology class, studying science, technology and society, when he saw a man enter the classroom with a gun for no apparent reason.

 Mr. Howell leapt to his feet, ran towards the gunman and tackled him, knocking him off his feet. His instant response didn’t prevent gunshots from being fired, but surely prevented a terrible situation from becoming much, much worse.

 Four students were injured in that anthropology class. Two were killed: 19-year-old Ellis “Reed” Parlier and Mr. Howell.

 “But for his work, the assailant may not have been disarmed,” Kerr Putney, chief of the Charlotte-Mecklenburg Police Department, said at a press conference. “Unfortunately, he gave his life in the process. But his sacrifice saved lives.”

 In Mr. Putney’s view, Mr. Howell was the “first and foremost hero” of this horrible incident.

 Kendrick Ray Castillo, 18, was a student at STEM School Highlands Ranch, a charter school in Douglas County, Colorado (in the Denver suburb of Highlands Ranch). He was watching the movie "The Princess Bride" this month with other students in their British literature class. He saw a fellow student arrive late and suddenly pull out a pistol, ordering everyone to stop moving.

 One of Mr. Castillo’s friends and classmates, Brendan Bialy, said that even during this period of confusion, Mr. Castillo made a “nonhesitation, immediate jump into action. The gunman was there and then he was against the wall and didn’t know what the hell hit him.”

 Several shots were reportedly fired, but Mr. Bialy — with the help of another student, Joshua Jones — was able to wrestle the shooter to the ground and take away his weapon.

 Mr. Bialy then turned his attention to Mr. Castillo. Unfortunately, he had been shot and was mortally wounded.

 “Kendrick Castillo died a legend. He died a trooper. I know he will be with me for the rest of my life,” Mr. Bialy told CNN.

 Mr. Castillo’s family spoke of his son's lifelong concern for other people.

 “I know that because of what he did, others are alive, and I thank God for that,” said his father, John Castillo. “I love him. And he is a hero and he always will be.”

 Such horrible attacks and infuriating deaths inevitably raise questions about our gun laws, and how people who should not have access to guns keep managing to get them.

 But it is important not to pass over the heroic acts of these young men. They saved countless lives.

 Messrs. Howell and Castillo weren’t famous. They will never be famous. (Unlike the Boston Marathon bomber, they did not appear on the cover of Rolling Stone magazine.) For the most part, people have since moved on to other news events. But both acted heroically in the most dire circumstances. They exemplified the courage and decency of unknown numbers of young Americans.

 We wish  to remember them and express our deepest sympathy to their loved ones.