Why is the story of Julius Caeser so much more well known than that of Augustus? What did Caeser have that Octavian didn't to have his legend perpetuated so?
Augustus had the benefit of riding on Julius' laurels (though was certainly plenty accomplished himself) while Caesar was born to a pretty humble clan of patricians. His rise was a lot more meteoric, and invokes very colorful imagery. The beloved general, the cunning barbarians, the hubris of rule, and finally, the betrayal by friends for freedom. Augustus ruled very peacefully after Antony was finished and 'hurried slowly', creating something great albeit quietly. I'd say he was more than Julius was, but Julius was the one who taught him.
Julius Caesar had much talent in leading his legions, which was noted in his Commentaries. Augustus relied on his lieutenants and the name given when Julius adopted him to get where he did.
Actually the earliest impressions made on Western man about Antiquity were largely shaped by the Matter of Rome by Jean Bodel, written in the 12th century, which was one of the three great cycles of medieval literature (along with the Matter of France and the Matter of Britain).
And most of that cycle is about Alexander the Great and Julius Caesar.
Not to mention that there's surviving documentation about him from other POVs, like Cicero's, that's very readable and well-written. Augustus was much more in control of what was written, so there's great literature created during his reign (Vergil is genuinely fucking sublime), but it's far more oblique in its commentary.
Caesar blows Augustus the hell out of the water in terms of charisma. Augustus is a brilliant thinker, administrator and politician in his own right but he never covered all the bases like Julius did.
Caesar was a brilliant general, a savvy politician and an unparalleled propagandist.
Octavian never had adventures with pirates in his youth. He never remained faithful to his wife, spitting in the face of the merciless and dangerous Sulla, etc etc.
Everything Caesar did in his life would have made an amazing 2 hour Hollywood blockbuster, and he did alot of things in his life.