"The Heterodyne Boys" refers to Bill and Barry Heterodyne in the legendary or fictional sense. The people of Europa know The Heterodyne Boys as a pair of brothers from a notorious family who became legendary heroes as a result of their many amazing adventures. As incredible as their real adventures were, and as heroic as the Boys really were, tales of their experiences were often exaggerated and simplified to the point of melodrama. These embellished tales then became a series of popular books and plays. The plays were put on by travelling Heterodyne shows, a form of entertainment so well-known that audiences knew the and to their favorite lines.
These tales were so common and so farfetched that Bill's own daughter, Agatha, at first had trouble thinking of the characters in them as real people. That is, until a relative of theirs [and hers], Theo, and the son of one of their chronicled companions, Z.
There is a sepia-toned card for The Heterodyne Boys in The Works. The Boys’ details are Heroes, Legends, and Sparks.
The Heterodyne Boys seem to have counterparts in other times and worlds, as can be seen here.