According to some authors Aiakos, who ends up as a judge of the dead in the underworld, was the son of Zeus and Europa. According to others (Pindar, Corinna) he was son of Zeus and Aegina (Or Poseidon and Aegina). When Poseidon and Apollo went to build the walls of Troy, they took Aiakos along to help them. A scholiast reports that it had to happen this way: since a mortal helped build the walls, they were not wholly invincible.

Pindar’s account of this emphasizes an omen that appeared at the completion of the walls. In his telling, Apollo interprets the omen as indicating that the descendants of Aiakos will be instrumental in the destruction of the city. Who are his descendants? Ajax, Achilles. Oh, Neoptolemos and Epeius the builder of the Trojan horse too!
(go here for the full Ode and a good commentary).

Pindar, Ol. 8.24-54

“For whatever weighs a great deal is hard
To judge with a fair mind at the right time.
But some law of the gods established this sea-protected land [Aegina]
As a sacred pillar
For every kind of stranger.
May rising time never tire
Of making this true
for this land tended by the Dorian people since Aiakos’ time.
It was Aiakos that Leto’s son and wide-ruling Apollo took
When they were going to build a wall around Troy. They summoned him
As a coworker for the wall. For it was fated that
When wars arose in the city-sacking battles,
That the wall would breathe out twisting smoke.
When the wall was just built, three dark serpents
Leapt up at it: two fell against it
and, stunned, lost their lives.
One rose up with cries of mourning.
Apollo interpreted this sign immediately and said:
“Pergamos will be sacked, hero, by your hands’ deeds:
So this sacred vision says to me
Sent by loud-thundering Zeus.
And it won’t be done without your sons: the city will be slaughtered by the first
And the third generations.*” So the god spoke clearly
And he rode Xanthus to the well-horsed Amazons and to the Danube.
The trident-bearer directed his swift-chariot.
To the sea by the Isthmus
Bearing Aiakos here
With golden horses,
Gazing upon the ridge of Corinth, famous for its feasts.
But nothing is equally pleasing among men.”

… ὅ τι γὰρ πολὺ καὶ πολλᾷ ῥέπῃ,
ὀρθᾷ διακρίνειν φρενὶ μὴ παρὰ καιρόν,
δυσπαλές: τεθμὸς δέ τις ἀθανάτων καὶ τάνδ᾽ ἁλιερκέα χώραν
παντοδαποῖσιν ὑπέστασε ξένοις
κίονα δαιμονίαν
ὁ δ᾽ ἐπαντέλλων χρόνος
τοῦτο πράσσων μὴ κάμοι
Δωριεῖ λαῷ ταμιευομέναν ἐξ Αἰακοῦ:
τὸν παῖς ὁ Λατοῦς εὐρυμέδων τε Ποσειδᾶν,
Ἰλίῳ μέλλοντες ἐπὶ στέφανον τεῦξαι, καλέσαντο συνεργὸν
τείχεος, ἦν ὅτι νιν πεπρωμένον
ὀρνυμένων πολέμων
πτολιπόρθοις ἐν μάχαις
λάβρον ἀμπνεῦσαι καπνόν.
γλαυκοὶ δὲ δράκοντες, ἐπεὶ κτίσθη νέον,
πύργον ἐσαλλόμενοι τρεῖς, οἱ δύο μὲν κάπετον,
αὖθι δ᾽ ἀτυζομένω ψυχὰς βάλον:
εἷς δ᾽ ἀνόρουσε βοάσαις.
ἔννεπε δ᾽ ἀντίον ὁρμαίνων τέρας εὐθὺς, Ἀπόλλων:
‘ Πέργαμος ἀμφὶ τεαῖς, ἥρως, χερὸς ἐργασίαι ἁλίσκεται:
ὣς ἐμοὶ φάσμα λέγει Κρονίδα
πεμφθὲν βαρυγδούπου Διός:
οὐκ ἄτερ παίδων σέθεν, ἀλλ᾽ ἅμα πρώτοις ῥάζεται
καὶ τερτάτοις.’ ὣς ἆρα θεὸς σάφα εἴπαις
Ξάνθον ἤπειγεν καὶ Ἀμαζόνας εὐίππους καὶ ἐς Ἴστρον ἐλαύνων.
Ὀρσοτρίαινα δ᾽ ἐπ᾽ Ἰσθμῷ ποντίᾳ
ἅρμα θοὸν τανύεν,
ἀποπέμπων Αἰακὸν
δεῦρ᾽ ἀν᾽ ἵπποις χρυσέαις,
καὶ Κορίνθου δειράδ᾽ ἐποψόμενος δαιτικλυτάν.
τερπνὸν δ᾽ ἐν ἀνθρώποις ἴσον ἔσσεται οὐδέν.

*First and Third generation: Aiakos had two sons (Telemon and Peleus) with Endeis and one with another woman (Phocus). Telemon and Peleus killed their half-brother; but the three sons fathered Ajax, Achilles and Panopeus (Phocus). The latter two grandsons fathered Neoptolemus and Epeios. Achilles’ son Neoptolemus helped take Troy; Epeios built the wooden horse.

Zeus – Aegina
|
Endeis – Aiakos – Psamathe
|                 |
Telamon Peleus                  Phocus
|                |                               |
Ajax       Achilles                  Panopeus
|                                  |
Neoptolemus                 Epeios