Thunderbolt of Zeus
According to Hesiod, there were originally three cyclops brothers-- Brontes ("Thunderer"), Steropes
("Lightning") and Arges ("Bright"). They were the children of Uranus and Gaia, and brothers of the Hecatonchieres (the Hundred-Handed ones) and the Titans. Uranus feared their strength and locked them away in Tartarus. When Cronus overthrew his father, he freed the three brothers from their prison so they would aid him in his conquest of Mount Olympus. However, just like his father, Cronus grew paranoid. He locked the cyclopes back into Tartarus, and began eating his children just to make sure someone did not try to stage a coup.
When the great Zeus freed his siblings from Cronus's gut, he turned to the cyclops brothers and honored them. In exchange, the cyclopes worked at the forge and crafted the Thunderbolts of Zeus, the Invisible Cap of Hades, and the Trident of Poseidon.
Today the three brothers work with Hephaestus at the forge, and create arms and armor of superb craftsmanship. Most magic items in the campaign that are not directly tied the Olympians was probably constructed by one of these Cyclopes.
Thunderbolt of Zeus
This javelin is a magic weapon. You gain a +2 bonus to attack and damage rolls made with this weapon. While attuned your attacks ignore lightning resistance, and you immunity to it as resistance. You gain resistance to lightning damage.
When this javelin is thrown, it transforms into a bolt of lightning, forming a line that extends out from you to a target within 120 feet. Each creature in the line excluding you and the target must make a DC 13 Dexterity saving throw, taking 8d6 lightning damage on a failed save, and half as much damage on a successful one. The lightning bolt transforms back into a javelin when it reaches the target. Make a ranged weapon attack against the target. On a hit, the target takes damage from the Javelin plus 8d6 lightning damage.
The Thunderbolt of Zeus’s property can’t be used against until the next dawn. In the meantime, the javelin can still be used as a Magic Weapon.