The Crown of Bethmora is an artifact featured in the film Hellboy II: The Golden Army. It is a magical golden crown that is a treasure belonged to the Bethmora Clan (includes King Balor, Prince Nuada and Princess Nuala) and the powerful legendary artifact that enables whoever wields it, to control the Golden Army.
In the distant tree when mankind declared war on magical creatures in spite of all species including humans living together under the mythical "tree of life" called Aiglin, the Father Tree, the Goblins of the lost City of Bethmora created the golden magic circlet that would be the namesake treasure of Bethmora to enable those of ancient bloodlines like that of King Balor to command the feared Golden Army. After the conflict ended with Balor arranging a peaceful coexistence between his kind and the human race, he divided the crown into three pieces with one third given to the humans while he kept the other two pieces. Only Balor's son Nuada considered this an error and refused to accept the truce as he enter an imposed exile.
Many centuries have passed and Nuada finally resurfaces, this time to declare war on mankind for their atrocities on the planet Earth. His crusade begins first with assembling the scattered pieces of the crown to have the Golden Army wipe out humanity for good. The first piece is reclaimed in 21st century New York City at a private auction house where many people including security being massacred as a first step in his genocidal campaign. Later he enters the hidden court of his father King Balor and slew the masked royal guards defending the elf king who then stands up from his metallic throne ready to accept his fate before being stabbed in the chest by his own son in the eyes of his family's shocked royal courtiers as the renegade prince claimed his fragment. His sister Nuala possessing the last piece of the crown escapes and enters the protection of the B.P.R.D. agency. However Nuada eventually finds her and invades the Bureau with ease, but was unable to retrieve the fragment as Nuala had hidden it and he was forced to retreat with his sister from the Bureau security agents.
It was Hellboy's closet friend Abe Sapien that brought the final piece of the crown to Prince Nuada within the ruins of Bethmora in exchange for Princess Nuala's safety but the elf prince betrayed him and activated the Golden Army in the ruins of Bethmora. Despite their attempts during the fight against now-awakened Golden Army, the 4 B.P.R.D agents including the teleplasty expert Johann Kraus were unable to truly destroy the enchanted mechanical soldiers as they would reconfigurate themselves. Seeing no alternative left, Hellboy himself declared a challenge to Nuada, as only one of royal blood could challenge the right to wear the crown. Hellboy, being through his paternal lineage as the son of the Fallen One (the demon duke Azzael), which in Hell is considered royalty. In the end after Hellboy's final battle with Prince Nuada within the ruins of the city of Bethmora and the royal twin siblings' sudden but tragic deaths, fellow BPRD agent and Hellboy's pregnant wife Elizabeth Sherman used her pyrokinesis to melt the Crown of Bethmora which deactivated the Golden Army permanently.