RAGE:
 Sing, Goddess, Achilles' rage,
Black and murderous, that cost the Greeks
Incalculable pain, pitched countless souls
Of heroes into Hades' dark,
And left their bodies to rot as feasts
For dogs and birds, as Zeus' will was done. 
Begin with the clash between Agamemnon-- 
The Greek warlord--and godlike Achilles.

 Which of the immortals set these two
At each other's throats?
Apollo
Zeus' son and Leto's, offended
By the warlord. Agamemnon had dishonored
Chryses, Apollo's priest, so the god
Struck the Greek camp with plague,
And the soldiers were dying of it.