Jason Grace is the son of Zeus, and he's the first of our five—count 'em: five!—focal characters, making him the first of our wannabe heroes to face off against a challenge that is physical, mental, and emotional (oh my!).
At Odysseus' palace, Jason must confront the ghost of his mother. It's hard enough for us mortals to deal with parent problems, and it's even more difficult when your mother's spirit is right in front of you and she's displaying all of mom's worst qualities: abandonment, betrayal, a drinking problem.
But Jason sees right through her ('cause ghosts are transparent…get it?), and banishes her by saying, "I'm no child of yours" (3.62).
It's a critical moment in his maturation process, realizing that he can be his own person. Unfortunately, just as he realizes this, he's impaled through the torso with a magic sword.
The sword that turns Jason into a donut with a hole in the middle is made of imperial gold, which is "deadly to demigods" (4.37). Translation: not great.
Laid up with this injury, Jason spends many chapters resting in the Argo II with the rest of his demigod crew. But when the Argo II is besieged by wild winds, Jason has to jump overboard with Percy Jackson to get to the source of the problem, much to the dismay of his girlfriend, Piper. And, let's be honest: much to our dismay, too. Talk about suspense.
Jason can't breathe underwater, but he summons a wind to protect him in a bubble. Underwater, Jason and Percy battle a minor goddess named Kymopoleia, who wants to kill Percy because no one honors her. Jason makes a bargain for Percy's life by promising to build her some shrines. Smart move, right?
This action shows that Jason is as brainy as he is brawny. Plus, if Jason Grace makes a promise, even if it's to a whiny minor goddess, you know he'll keep it. He says early on that he "never wanted to abandon anyone the way he'd been abandoned and lied to" (3.29)…and that means he always honors his word.
Somehow, his honor magically cures that nasty sword wound, too.
Jason proves his might, too, in the final battle with the giants at the Acropolis. And to bookend Jason's parental issues, he finally gets to meet his dear ol' dad: Zeus, the king of the gods. Not only that, but Zeus even compliments his heroic son: "You have proven yourself a true hero" (49.48).
So while Jason definitely didn't start off as a zero, he ends up a hero…and then some.