It's fun to imagine what our characters might have been like before the times that are depicted in the strip. It's an empty canvas. We can invent any chronology we want.
In the Sunday page above, Sarge shares some of his early dreams with Beetle. Like many kids, he started out wanting to be a cowboy. Later on, as he got more athletic, options like football player and wrestler became more desirable.
After becoming a Top Sergeant, all he wants now is to be obeyed.
Here is a Sunday page from 2002, in which we invented Lt. Flap's history of hero worship.
Since Beetle started out as a college student, some of the details about his life before Camp Swampy have been documented. Here is an episode, in which Beetle goes back to visit his old campus.
Of course, once we fill in these details, our readers expect us to be consistent. We are not allowed to contradict their backstories, even if they are made up.
– Brian Walker