The Metal Demons (often called Demons for short) were a villainous race of creatures featured in the first installment of the Wild Arms series (and later Alter Code: F). They are made from a living metal (which was later used to create the Holmcross to combat the demons themselves) and are native to the planet Hiades. Their leader is the Demon Queen, Mother. Mother destroyed Hiades in her insatiable desire to destroy.
The Demons made the move to Filgaia 1,000 years before the events of the original Wild Arms. They began a war with the Elw and Human races, hoping to colonize the planet as their own. The Elw eventually warded them off, but not before fleeing Filgaia themselves and setting up home in the Elw Dimension. The Demons went into hiding for the next 1,000 years.
They next were seen attacking Arctica Castle approximately 10 years before the events of Wild Arms. The Kingdom was silently destroyed and all died except for two, Jack (who escaped and began his quest for revenge) and Elmina, who was turned into the Demon Lady Harken by Alhazad. The Demons attacked Arctica to reclaim their lost Queen, Mother, who was trapped in a cocoon in the castle, her heart ripped into three pieces and placed all over statues in Filgaia.
The Demons next attacked the the Ruin Festival in Adlehyde, killing many and also succeeding in abducting three golem statues the Elw used in the first war: Lolithia, Barbados and Diablo. Lolithia and Diablo were both used to fight against the main characters, and Barbados was trashed in the sand sea, too catatonic to contain in the confines of the Photosphere. The Demons were also successful in stealing, using, and recreating the all powerful Tear Drop crystal, stolen from Cecilia in the battle of Adlehyde.
The Demons then destroyed all three statues which housed Mother's heart. Mother was revived and instantly returned to her insane passion to see all life end. She admitted that she was the one who destroyed the Demons' home planet, Hiades, in which was only a pitstop before Filgaia. The Demon leader of the Quarter Knights, Zeikfried, saw his Mother for what she was and deemed her to be destroyed. Zeikfried helped the main characters retrieve the Tear Drop and also to kill Mother.
Following this, Zeikfried was returned to his Mother following the scuffle in the Gate Generator. He was eaten by the remains of Mother and began to metamorphose into her, beginning attempts to destroy Filgaia, rather than subjugate it. His Demon partner, Alhazad, realized Zeikfried had changed, but was ordered to do as he was told.
Each Demon was killed off individually by a main character. Berserk (or Belselk in WA1) was killed by the Demon Boomerang and subsequently took his place as a member of the Quarter Knights, Alhazad was destroyed by Rudy, Jack and Cecilia, Lady Harken was killed and exorcised of her demonic possession by Jack, Boomerang was killed by the party at the Ancient Arena, and Zeikfried was killed by the party in cyberspace, following his transformation into Motherfried (after Mother possessed him) and escape from Hell.