Featured in Marvel Comics, the Legacy Virus was a biological weapon engineered and released by the madman Stryfe for the purpose of killing all mutants. The "plague" -- as it was called -- lasted for years and killed many mutants. The virus was cured when Colossus -- a mutant who is almost invincible when a thick, silver metal covers his skin -- sacrificed himself so that the "cure" to the Legacy Virus could go airborne.
Symptoms of the Legacy Virus included purple lesions, coughing, fever, sweats, swollen glands, cardiac arrest and uncontrollable mutant abilities. Mutant abilities aside, many of the symptoms were eerily similar to those experienced by people living with HIV/AIDS. Given mutants' "outcast" status in the comic book universe, many saw the Legacy Virus storyline as a metaphor for HIV/AIDS in the LGBT community.