The Daggers are designed to kill the Antichrist, and were made in Megiddo, where Christianity began. It is implied in the novelization of The Omen that the Daggers were created by an ancestor of Carl Bugenhagen circa 1024 AD, as a means of destroying Satan's progeny.
The Seven Daggers were excavated in Tel Megiddo by Carl Bugenhagen. When Robert Thorn and Keith Jennings come to him looking for a way to kill the Antichist, Bugenhagen gives them the Daggers of Megiddo and explains how to use them to kill the Antichrist. Afterwards, Robert refuses to kill Damien as he has raised him as his own son, and throws the Daggers away. When Jennings goes to retrieve the Daggers, he is decapitated in a freak accident. Robert then decides to kill Damien after all, and takes the Daggers back to London with him.
In London, when Robert discovers that Damien is indeed the Antichrist, he kidnaps him and takes him to a church. On the church's altar, Robert prepares to kill Damien with the Daggers, but at the last second before Robert can stab Damien, police arrive and shoot and kill Robert.
According to the novelization of the original version of the film, after Robert was killed, the priest of the church where Robert tried to stab Damien had the Daggers of Megiddo sent back to Bugenhagen in Israel.
A week after Robert Thorn's death, Bugenhagen gives his old friend Michael Morgan a box containing the Seven Daggers of Megiddo and a note explaining that Damien Thorn is the Antichrist. When Bugenhagen takes Morgan to Yigael's Wall in the ruins of (what appears to be) Megiddo, the ceiling collapses and the two are buried alive with the box containing the Daggers of Megiddo.
The Daggers remain buried inside the box for seven years, until the box is unearthed and sent to the Thorn Museum in Chicago. When Dr. Charles Warren opens the box, he discovers the Daggers of Megiddo inside along with the note explaining that Damien is the Antichrist. He leaves the Daggers in a drawer in his office at the museum, and goes to Richard with the note.
Some days later, when Richard searches Warren's office for the Daggers of Megiddo, Ann finds the Daggers in the drawer and stabs Richard with them.
Damien then blows up the Thorn Museum's boiler, killing Ann and destroying the museum.
After the Thorn Museum was burnt down by the fire Damien caused, the Seven Daggers of Megiddo remained buried in the ruins for twenty years, until they are found in the rubble by a construction worker during a reconstruction attempt. The worker sells the Daggers at a pawnshop, where they are bought and put up for auction. When the auctioneer who buys them researches the Daggers and realizes what they are, he hands them over to a priest, who in turn sends them to Father De Carlo in Subiaco.
De Carlo divides each of the Seven Daggers among himself and his six priests, and they then travel to London to hunt down and kill Damien Thorn with the Daggers. At an interview between Damien and Kate Reynolds, Brother Benito tries to stab Damien with his Dagger of Megiddo. However, he is killed when he falls and is caught in plastic that catches fire. Damien then takes his Dagger.
Some days later, Brother Matteus lures Damien across the countryside of England to an old ruin, where Brothers Paulo and Martin plan to ambush him with their Daggers. However, Damien causes Martin and Paulo to hallucinate Matteus as him, causing the two to stab him instead. Damien then leaves Paulo and Martin trapped under a grate to die, and takes their three Daggers of Megiddo.
One day, Brothers Simeon and Antonio lure Damien onto a bridge while he is participating in a fox hunt, but Damien easily kills them and takes their two Daggers. Some days later, when Kate reluctantly takes Damien and Peter to an old ruin to find Christ, De Carlo ambushes and tries to stab Damien with his Dagger of Megiddo, but Damien uses Peter as a human shield against the dagger.
Enraged at her son's death, Kate pursues Damien through the ruin with De Carlo's Dagger, and attacks and stabs him with it, fatally wounding him.
The Daggers of Megiddo are designed to kill the Antichrist. One of the Daggers extinguishes the Antichrist's physical life force, while the other six extinguish his spiritual life. In order to destroy the Antichrist forever, the Daggers must be stabbed in his chest in a sequence that forms the cross; the Dagger that extinguishes physical life must serve as the centre of the cross that the Daggers form.
The ritual must also be carried out in a church, and the Antichrist must die on the church's altar. However, if the ritual is not carried out this specific way, then while the Antichrist's body may die, his soul will survive and live on.