In Heinlein's Space Cadet, there are four names added to every roll call, with others answering for them. Those names are Dahlquist, Martin, Rivera, and Wheeler.
Dahlquist is the protagonist of The Long Watch, a short story by Heinlein. His story is summarised in Space Cadet as follows:
Matt pressed the button; the alcove filled with the first bars of Beethoven's Fifth. The music gave way to a voice: "The Patrol was originally made up of officers sent to it by each of the nations then in the Western Federation. Some were trustworthy, some were not. In 1996 came a day shameful and glorious in the history of the Patrol, an attempted coup d'etat, the so-called Revolt of the Colonels. A cabal of high-ranking officers, acting from Moon Base, tried to seize power over the entire world. The plot would have been successful had not Lieutenant Dahlquist disabled every atom-bomb rocket at Moon Base by removing the fissionable material from each and wrecking the triggering mechanisms. In so doing he received so much radiation that he died of his burns." The voice stopped and was followed by the Valhalla theme from Götterdämmerung.
Rivera's story is told in Space Cadet:
Matt thought about it, fiercely. He remembered Commander Rivera — one of the Four, of the proud Tradition — how Rivera, sent down to reason with the official in his own capital, his very native city, had kept the trust. Suspecting that he might be held as hostage, he had left orders to go ahead with the attack unless he returned in person to cancel the orders. Rivera, whose body was decaying radioactive dust but whose name was mustered whenever a unit of the Patrol called the roll.
Both Rivera and Dahlquist have sacrificed themselves, upholding the values of the Patrol.
But who are the other two, Wheeler and Martin? Why are they honoured?