The Spear of Osiris was a collapsible golden spear that, when opened, could be used to defeat supernatural creatures, namely the Scorpion King, an ancient warlord that was bound to an ancient curse as dealt by Anubis. The Spear of Osiris is solely effective against Egyptian Monsters such as Winged Scarabs, Cursed Mummies, Sphinxes, demons, devils, Fallen Angels, Evil/Unholy Ones/Ghosts, Dark/Demonic/Evil Entities, The Left, Infinite Lucifers/Satans, Dark/Evil Gods, The Evils of both mankind & Planet Earth, etc.
The Spear of Osiris was created in ancient Egypt as the only weapon that could impede the Scorpion King’s return to life: whoever killed the Scorpion King, the legends told, would claim possession of his armies and could decide to either use it to destroy mankind or to lay down its power.
The Spear had resided in the ruins of Hamunaptra for some time before it was unearthed by a thief named Beni Gabor in 1926 A.D when Beni had attempted to loot the ruins but had died in the attempt: Beni had filled one sack with golden treasures before mounting it on a nearby camel and Beni had returned to take more treasures but ended up trapped inside the ruins and eaten by scarabs. Others, however, had escaped Hamunaptra: the explorer Rick O'Connell and the archaeologists Evelyn and Jonathan Carnahan, and the three had helped themselves to the treasures left in the saddle-bag of one of the camels that they used to leave the ruins.
Time in England
The Spear ended up with Jonathan, who boasted for years afterward that the Spear was all that remained of his fortune after some “rather unscrupulous characters” had taken a substantial part of it.
One night, Jonathan was house-sitting for the O'Connell family, but brought home a lady friend and began to fabricate the story of how the cursed mummy Imhotep was defeated several years before, and how Jonathan had taken “his gold sceptre” as a prize.
As the two meandered about O'Connell Manor, Jonathan elaborated further, at which point several robed thugs seized Jonathan, forcing him into an armchair and forcing Jonathan’s lady friend out. The thugs were all members of a cult, led by Baltus Hafez, the curator of the Egyptian wing of the British Museum of Antiquities. Hafez confronted Jonathan, asking about the Bracelet of Anubis, thinking Jonathan to be Rick O'Connell himself, but got distracted once he saw the Spear of Osiris in Jonathan’s grip and snatched it away.
At that moment, another cultist entered the room. A tall, thin woman clad in a black gown, she also took Jonathan to be O'Connell much like Hafez had, and so she drew out an Egyptian Asp snake from a basket that she had brought to the manor. Before the snake could strike, however, the real Rick O'Connell entered the room and admonished the cultists, thinking them to be nothing more than house guests of one of Jonathan’s “wild parties”. The cultists attacked with the asp, throwing daggers and finally firing machine guns at O'Connell and Jonathan, but not before Jonathan stole back the Spear from Hafez’s grip.
Return to Egypt
Jonathan took the spear with him all the way to Ahm Shere. Upon reaching the Scorpion King's lair, Jonathan and his nephew Alex met up with Rick as he was being chased by the Scorpion King in his chambers.
At some point during the chase, Rick noticed several carvings depicting the Spear's true function. With the brief time he had, O'Connell told Jonathan how to activate the spear before he resumed running from the Scorpion King.
Once he activated the spear, Jonathan intended to throw it at the Scorpion King, but when he tried, Imhotep caught it and hurled the spear at the Scorpion King himself.
Instead, Rick caught the spear before it could pierce the Scorpion King and ran him through, ordering him to take the Army of Anubis back to the Underworld with him. Presumably, the spear went to the Underworld when the oasis was swallowed up by the desert.
- In the movie, the Scorpion King 2, the spear was said to also destroy other Egyptian monsters.