Fathom Five is a team of super-powered Atlanteans who serve as the strike force for an extremist religious movement in Atlantis known as At’la’tique. Nagala and Shakkoth, the apparent founders of At’la’tique, took the name (meaning “fury of the sea”) from the ancient writings of Atlantean poet Numara D’athahr. Their cult seeks not only to remove King Namor from his throne, but to assault the surface world as well in hopes of sparking a global war. To this end Nagala recruited several super-beings to form the strike force Fathom Five: Llyron, an artificially-aged offspring of Namor and Llyra who once tried to depose his father; Dragonrider, who uses a mystical talisman resembling the Horn of Proteus to command giant sea monsters and having previously fought against Namor when she felt he had turned his back on his poorer subjects; the mysterious Sea Leopard, who may have been part of a race of sea-dwellers known as the Ancients and lived in the remains of Old Atlantis; Bloodtide, an Atlantean woman mutated by pollution who can control water; and Manowar, a bizarre creature resembling a jellyfish.
Fathom Five secretly allied themselves with Baron Strucker’s Hydra and launched terrorist assaults on various countries, including one in the Persian Gulf. They then attacked Beijing before turning their attention to the United States. Attacking New York City, Fathom Five were opposed by the newly-reassembled Thunderbolts. The two teams fought to a standstill until the arrival of Captain Marvel (Genis-Vell) routed the Atlanteans. Fathom Five fled into the nearby bay and escaped capture. As Namor attended a United Nations meeting to assure the surface world that his nation was not behind the At’la’tique attacks, Fathom Five regrouped near Atlantis. However, because of their assault on New York, Namor ordered his military to flush out and round up the cult members. This led to a confrontation between Fathom Five and the Atlantean troops, many of whom died fighting the rebels.
Fathom Five launched a second attack on New York, battling the former Avenger member Warbird and her associate Abe Jenkins, who tried to contact his Thunderbolts team for aid. Several Thunderbolts finally arrived and turned the tide of the battle. The Radioactive Man defeated and attempted to kill Llyron for the attack in China, but Jenkins, wearing his old Beetle armor, talked him out of it. Before Fathom Five could be finished off, the terrorist group Hydra launched its own assault on New York City. By the time the Thunderbolts and several other heroes defeated Hydra, Llyron and Sea Leopard had escaped. Bloodtide, Dragonrider and Manowar were taken into custody shortly thereafter. Unbeknownst to Llyron, the Radioactive Man had infected him with radiation poisoning , hoping he would take it back to At’la’tique and infect their other members. Instead, Llyron was arrested by Atlantean guards and brought the poison into Atlantis. Namor sought out the Thunderbolts to stop the spreading radiation, hoping to force Radioactive Man to purge the energy. He did so, cleansing Atlantis of the radiation, but secretly left a modified, slower-acting version of the radioactive contamination on Tamara Rahn, Namor’s spy within At’la’tique (this would not harm Rahn herself, but would gradually affect and kill those around her). Whether or not Rahn returned to the At’la’tique base after this is currently unknown.