Helm of Darkness

The Helm of Darkness is the weapon made especially for Hades (deity) during the war known as the Titanomachy, in which the gods defeated the Titans and sent them to Tartarus.The helmet was made of pure dogskin, and a pair of wings were attached to it, one on each side, so as to resemble the helmet of the god Hermes. It rendered its wearer invisible.

Perseus

When the youth Perseus was sent to fetch Medusa's head by the evil king of Seriphos, Polydektes, he was surely in need of some sort of miracle in order for him to complete such a task. He was visited by his half-sister, the goddess Athene, and her half-brother Hermes, who aided him by giving him part of the equipment needed: Athene gave him her polished shield (Aegis) to act as a mirror (this helped Perseus so as not to look directly at Medusa but rather at her harmless reflection in the shield), and a pair of winged sandals by Hermes (other versions say that Hermes gave him the harpe, a sickle-like sword of immense sharpness and strength).

The helmet of darkness appears later, when the youth visits the Gorgons' sisters, the Graeae, for directions to the Stygian Nymphs (others say the Hesperides) in order to collect the rest of the equipment needed, and the way to Medusa.It is definite that the helmet was lent to the nymphs by Hades, who gave it to him along with the harpe and the kibisis, a magic goatskin wallet, capable to grow or shrink according to the size of its contents, and the only container capable of harmlessly holding Medusa's venemous blood. Since Medusa's sisters, Sthenno and Euryale were immortal, the helmet of darkness played a very important part for Perseus' quick and undetected escape from the horrible sisters.

After his task completed, Perseus returned his weapons to Athene, who then saw that all went back to their rightful owners.