Let's examine the symbolic significance of what happens in this final episode. Why did Billy's Grampa B.J. have to come along and spoil all their fun? Because that's more or less how it happened in reality ["Reality?!", I hear you splutter? Allow me to explain:] - id software decided to axe the Commander Keen series in favour of their next ground-breaking project, Wolfenstein 3-D. In short, Wolfenstein killed Commander Keen.
Perhaps unwilling to let the legend of Keen go entirely, the id guys decided to make the hero of Wolf3D be Commander Keen's grandfather. The following is an extract from The Apogee FAQ:
William Joseph Blazkowicz was born August 15, 1911, to Polish immigrants, Blazkowicz was a top spy for the Allied Forces, receiving the Congressional Medal of Honor and other accolades for heroism. He completed countless missions during his outstanding career. "B.J.", (as he was called by his friends) married after World War II, at age 40, to Julia Marie Peterson. Their son, Arthur Kenneth Blazkowicz, became a television talk show personality in Milwaukee. For show biz purposes, Arthur changed his last name to Blaze. Arthur later married Susan Elizabeth McMicheals. They had one son, which they named after Arthur's father, William Joseph Blazkowicz II, or as he signs his grade school homework, B. Blaze...
Another bit of self-referent symbolism is B.J.'s final comment, "It's time you grew out of such childish things anyway!" - probably what most people would say to the ageing Keensters who still enjoy a good go at the old CK games every now and then.
And then, of course, we see that Commander Keen is not only forced to give up his brother's helmet (to now be used for purposes much more noble than -pfft- saving the Universe, no doubt) but that his amazing Martian Pogo Stick has also been destroyed in the explosion of the self-destructing Big-Bang-A-TronTM. The irreversible transition from Commander Keen to Billy Blaze is thus complete. Q.E.D.!
But it doesn't end here, despite what the words at the bottom of the cartoon say!
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