According to myth, Amalthea was the nurse of Zeus during the years he was growing up hidden from his father Cronus in a cave on Crete.
The goat Amalthea suckled the infant Zeus and, together with Melissa and the legendary Curetes, aided in the eventful birth and upbringing of the greatest of the Twelve Gods of Olympus, so that he would grow up to claim and attain his authority as ruler of the cosmos
The Horn of Amalthea
The myth also tells us that one day, as Amalthea played with little Zeus, he accidentally broke off her horn. To make up for it and as a sign of gratitude, Zeus made the broken horn always be full of whatever its owner desired. It became known as the Horn of Amalthea or the Cornucopia, an eternal symbol of abundance.
Heracles and the Horn of Amalthea
In a later legend, Heracles or Hercules, the son of Zeus, owned the Horn of Amalthea. Heracles fought the river-god Achelous in single combat for the heart of Deianira, who later became his wife.
During the fight, Heracles broke off the horn of Achelous, who gave up the contest for Deianira.
The hero gave the defeated Achelous his horn back and, as an apology, the Horn of Plenty, i.e. the Horn of Amalthea
The aegis, the shield made from the skin of Amalthea
When Zeus grew up and sought to overthrow his father Cronus, this was not a bloodless affair. He had to face the Titans, who ruled the universe under Cronus. Legend has it that the Titanomachy, the War of the Titans, ended in the dethronement of Cronus and the victory of Zeus and his siblings, the gods of Olympus.
In that fight Zeus needed a suitable shield (or armour, according to others), which would be invulnerable and terrifying to look upon. Hephaestus made this shield from the skin of Amalthea, which could not be pierced by arrows, and placed on it the head of the Gorgon or Medusa, which turned all those who looked on it to stone.
After the great war for absolute authority, Zeus gave his armour, or aegis (meaning “goat-skin”), to his daughter Athena, the goddess of wisdom.