Origin

Fabian Cortez organized the original Acolytes, who pledged themselves to Magneto and his cause. Cortez was always goading and manipulating Magneto into combat with humanity and the X-Men at every turn. This would lead to the destruction of Magneto's space-station Asteroid M and the deaths of the other Acolytes including Cortez's own sister Anne Marie.

With the belief that Magneto was dead, Cortez then recruited a new group of Acolytes to follow him in Magneto's name. Now worshipping Magneto as the Acolytes god. They launched several strikes on humanity, ranging from attacks on a military base where new Sentinels were being built, to slaughtering helpless humans in a hospital. However Magneto eventually resurfaced, sending his chosen heir Exodus, to inform the Acolytes of Cortez's betrayal. The Acolytes welcomed Exodus as their new leader, and Cortez was left behind.

Cortez fearing Magneto's wrath fled to Genosha. Still claiming to speak in Magneto's name, he incited the nation's mutate population into starting a civil war against the humans, the world's first instance of the long-threatened genetic war between man and mutant. With the aid of the mutates, Cortez kidnapped Magneto's granddaughter Luna, intending to use her as a shield to protect himself from Magneto, the X-Men and the Avengers. Cortez was unaware that Magneto had recently been mindwiped by Charles Xavier and Exodus came to Genosha in his place with plans to kill Cortez.

Cortez reappeared months later claiming to have been badly injured yet not actually killed despite all appearances. He manipulated Joseph into posing as Magneto, pitting him against Exodus in an attempt to regain control of the Acolytes. Despite his scheme's failure, he was allowed to return to the team. Months later, at a time when Exodus had briefly been imprisoned, the Acolytes split into two groups, each searching for Magneto. Cortez led one group, but they abandoned him during a battle with the X-Men, upon realising how he had been using them for his own purposes.

Alone again, Cortez was surprised to be recruited by Magneto himself, who was given control of Genosha, by the United Nations. Seeing as how Fabian Cortez had betrayed him earlier, Magneto had only let Fabian Cortez serve him on Genosha because his powers had been reduced and Cortez's mutant power was to heighten the abilities of other mutants. After Magneto was restored to full power by one of the Genegineer's machines he no longer needed Cortez and pulled him from a prison in Hammer Bay fifty miles to Carrion Cove in less than 20 seconds. The impact seemingly killed Cortez instantly, although this is not the first time he has been believed dead, and a connection between Cortez and Mr. Sinister had just been revealed.

Powers

His principal ability was to enhance other mutants powers, even to the point of going out of control. He was highly intelligent and an able military strategist. Cortez was also a skilled martial artist, but often carried a gun.

Alternate Realities

Earth-2149

In the Marvel Zombies reality Fabian Cortez was one of the few people on Earth not turned into a zombie.  He was the leader of the surviving Acolytes and led them back to Earth to find Magneto.  They instead find Black Panther and bring him back to Asteroid M.  Years later the survivors return to Earth after the Zombie Galacti left.