|The following is based on Fallout: Brotherhood of Steel and has not been confirmed by canon sources.|
Yes, we are many. A mutant army. The destruction of our Master has only strengthened our resolve. We will control this vault - and its scientific secrets - then use it as a base of operations for our war on humanity.”— Attis
Attis is a highly intelligent super mutant and was an important commander in the Master's army. After the destruction of the Master and the vats, he created the "Attis army" from the large remnants of the Master's army. He then began searching for clues regarding the history of FEV before trying to make the Master's plan a reality.
Attis is one of the few super mutants with great strength, both intellectual and physical like the Lieutenant or Marcus. He is tall, strong, and quite athletic for a super mutant. He is also very fast and knows how to use all kinds of weapons. He was a Mariposa super mutant and one of the Master's commanders. After the death of the Master and the destruction of the vats, he created and became the general of the faction which tried to continue the Master's work, rebuild the army and transforming the entire human race into super mutants for having a single race, able to survive - thrive in the Wasteland, eliminate the differences and removing all discord.
After Attis had created his own army, he took his group into hiding, searching for clues regarding the history of the FEV virus. Throughout the years, he and his army led a guerrilla war against the Brotherhood of Steel (still looking for the rest of the mutant army because of the failure of the Airship's expedition that created the Midwestern Brotherhood of Steel), eventually forcing Rhombus to start a crusade named "Texas Expedition" in order to annihilate the remaining super mutant threat.
Attis learns about a secret Vault-Tec installation called the Secret Vault, the Vault-Tec private Vault after the Great War, with new and possibly improved versions of the FEV virus. He led his group to the ghoul city of Los in Texas, where the Secret Vault was located. His first goal was to rebuild the mutant army and develop a cure to mutant sterility. The Secret Vault gives him hope, as the Vault scientists' researches was dedicated to improving the original FEV in order to maintain reproductive functions.
Arriving in Los, he tried to negotiate with the Church of the Lost, the cult that controls the city, but in vain. Just some time later, a contingent of Paladins of the Brotherhood of Steel lead by Rhombus arrived and a battle broke out between the Attis army, the Church of the Lost and the Brotherhood Paladins. The Brotherhood of Steel group was annihilated and Rhombus was captured. Attis used this confusion to his advantage and managed to get into the Secret Vault. But to access the laboratory section, he had to get a key card, only possessed by the Church of the Lost.
Triggering a siege on the city to get the key card and going to war with the Church of the Lost, he continued to prepare his plan and allied himself with Jane, the raider Matron of the largest and most powerful raider gang of Texas located in Carbon. She selling human slaves to him from raids in Carbon, and he goes in Carbon himself to retrieve them personally. They now becoming slaves of Attis but their function remained unknown in his army (perhaps he wanted to transform them into super mutants after tested and accessed to the modified FEV).
Continuing his plans for the war against the Church of the Lost and to get the key card, the Initiate changed the deal, destroyed a weakened Church of the Lost, kill Blake the high priest of the cult and comes to the Secret Vault to destroy both the Attis army and the Secret Vault with the key card stolen and hidden by Rhombus, preventing Attis to exhausting his army in a long drawn-out siege. Refusing to give him the key card, Attis engaged the combat, using his retractable arm blade to fight. Though he loses, two nightkin appear and quickly stuns and capture the Initiate. Taking him to an area with a huge pit down to the Secret Vault ruins, Attis took the key card, cuts off his arm and commands the nightkin to throw him into the pit. However, thanks to Mary, the Initiate managed to survive and later even received a new arm through a regeneration experiment.
Attis penetrates deeper into the Vault, until the last section of the laboratory, the laboratory core and found the Vault-Tec modified FEV. Just before the Initiate arrived and the combat start, he tested it on himself, it was revealed that this FEV is unable to make mutants fertile. However, an unforeseen consequences followed, revealing another potential of the Vault-Tec modified FEV, it led to a strange side effect and his skin turned darker. During the battle, he mutates again, increases and reaching the size of a super mutant behemoth and he cured of all these injuries. After seriously injured by the Initiate again, the modified FEV proves highly unstable, causing Attis to regenerate uncontrollably due to the amount of damage he receives. He explodes and decomposes into a strange organic biomass, a rapidly-multiplying multicellular organism that covers the entire laboratory section of the Secret Vault. Though initially he believed his discovery leads to nothing, now he begins to realize the new potential of the virus.
This new creature begins to grow with each second, and it's various organs, like eyes, mouth, and tentacles begin to appear out of the floor. This organic nightmare retains some consciousness of Attis, now starting to dream of a new world, similar to the Master's Unity. In this gigantic form, Attis tried to make the remaining super mutants found in the Secret Vault "join" him, but they were scared of him and began to fight back. The Initiate ran from him, fighting his tentacles, his giant "heads" with one eye, and several fleshy walls with big mouths in the center of them. Eventually, he found Patty, the vault security officer, who now was enveloped in a cocoon-like state by Attis and is being slowly digested. She reveals that there is a way to start a self-destruct sequence, and asks the Initiate to kill her. In the next room, the needed terminal is found, and the Initiate escapes using the Vault's monorail, while the Vault's nuclear warhead, specially designed for this purpose, detonates, and killing Attis forever.
- Attis seems to collect the skulls of some of his victims. 2 skulls are seen hanging on two sticks he carries on his back and two others hanging to his hair. He also expresses a desire to collect the players skull should they anger him.
- While his mutations due to the Secret Vault modified FEV transforming him into a multicellular mutant is similar to the Master, they are still different creatures.
- Attis is probably named after the consort of Cybele in Phrygian and Greek mythology, Attis.
- As can be seen in the remnants of the Master's army encounter in Fallout 2, such factions did indeed exist.
- "Ah, at last I meet the mouse who stalks lions. I am Attis, a general in the mutant army... and you have something I need, little mouse."
- "Your humans are easily manipulated. After the unfortunate business with the psycho ghouls, it was easier to let you bring me the key rather than enter a long, drawn-out siege on the city. I have other plans for my army."
- "Yes, we are many. A mutant army. The destruction of our Master has only strengthened our resolve. We will control this vault - and its scientific secrets - then use it as a base of operations for our war on humanity."
- "The vault laboratory holds... let's just say it is a weapon. One that will give the mutant army a great advantage in our war against humanity."
- "Enough talk! Does the lion hold conversation with the mouse in the wild?!? Your natural function is to succumb to the lion's will. Give me the key!"
- "Is that an invitation to battle? How amusing! After I take the key from you, I will make a special decoration of your skull!"
- "Fertility. That's what we came for. The research in this vault was centered around curing fertility due to mutation. Imagine, then, a treatment that allowed mutants to reproduce, to breed. That would truly be a weapon!"
- "I will restore the dead world, blanketing it with life, removing all discord. It will be a perfect world."
- "And it was given unto the beast to make war with the saints, to overcome them... and power was given him over all kindreds and tongues and nations..."
Attis appears only in Fallout: Brotherhood of Steel.