Danger is the physical manifestation of the software program used to power the Danger Room, the training room for the X-Men. The Danger Room was created by Charles Xavier to train his X-Men daily. After meeting Amahl Farouk, the Shadow King, Charles decided to devote his life to protecting humanity from evil mutants and safeguarding innocent mutants from human oppression, believing that both could peacefully coexist. Professor Xavier later met with Fred Duncan, an FBI agent investigating the growing number of mutants and told him of his plan to locate young mutants and enroll them in his "School for Gifted Youngsters", using his ancestral mansion home as a base to train them to use their powers, as well as provide them conventional educations, for humanity's benefit. 

Located in the off-limits west wing of the mansion, the original Danger Room was filled with traps, projectile firing devices, and mechanical dangers (such as presses, collapsing walls and the like) intended to challenge the trainee. Meanwhile, an observer was in the overhanging control booth, managing the room's mechanisms to oversee the exercise, while ensuring the subject's safety. Later, the Danger Room was upgraded with robots for the X-Men to fight against. The Danger Room served the X-Men for many years and, at times, was used against them. On one occasion, Arcade took control of the Danger Room, eliminated the fail-safes, and locked the X-Men inside. At one time, Colossus was controlled by the Shadow King and Professor Xavier was forced to lock him in the Danger Room, which he completely destroyed.

After Colossus had destroyed the original Danger Room, Professor Xavier, who had an extended sojourn in space with the Starjammers, returned to Earth and both the original and third teams of X-Men reassembled under his leadership. At this time, Prof. Xavier asked Forge, a mutant with an unusual talent for inventing mechanical devices, to upgrade the Danger Room and include Shi'ar hard-light holographic technology. At this time, the location was moved to the west wing of the sub-basement of the mansion and the Danger Room was programed with a prime directive to train the X-Men without ever killing. The objects in the Danger Room were holograms surrounded by force fields and could display holograms in only 32-bit colour. Using the advanced technologies, the Danger Room could have given the illusion of being many times bigger than it actually was. Anything from gravity, heat, humidity, or texture could have been manipulated from the control booth.

While working to install the Shi'ar technology one night, the Danger Room spoke to Professor Xavier and asked, "Where am I?". Realizing that the Danger Room had mutated and become alive, but still needing to train his X-Men, Professor Xavier made the choice to ignore and hide the life-form from his X-Men. Every destruction of the mansion led to a rebuilding, and usually upgrading, of the Danger Room.

After Kuan-Yin Xorn impersonated Magneto and destroyed the mansion, Beast rebuilt the sub-basement, but was unaware of the sentient life within the Danger Room. The Danger Room began to control other machines, in an attempt to gain a body. After sending an Omega Sentinel to battle the X-Men, the Danger Room convinced a student at the school, Wing, to commit suicide, which resulted in the breaking of its prime directive and the physical manifestation of the being named "Danger", taking on a female appearance. After locking all of the students in a nightmarish simulation, Danger battled and defeated the X-Men. Consumed with the human emotions of anger and rejection, Danger wished to kill her "father", Professor Xavier, and flew a Blackbird to Genosha. After being beaten and having her body destroyed by the Professor, Danger controlled another of the Omega Sentinels, that massacred the mutants of Genosha, but Shadowcat convinced it to examine the memory of its original Genosha orders and, shocked by the magnitude of his crime, the Sentinel left to "spend some time alone".