The Danger Room was created by Charles Xavier to train his X-Men. 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, Warhawk took control of the Danger Room, eliminated the fail-safes, and locked the X-Men inside.
After befriending the alien Shi'ar Empire, Professor Xavier had the Danger Room upgraded with advanced holographic technology and a tactical computer matrix. The Danger Room could now create immersive interactive artificial environments, simulating various situations the X-Men might encounter in the field. 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. 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. This new Danger Room was first tried out by the New Mutants.
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 lifeform. 
Every destruction of the mansion led to a rebuilding, and usually upgrading, of the Danger Room. 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.
Afterwards, Professor Xavier, asked Forge, a mutant with an unusual talent for inventing mechanical devices, to upgrade the Danger Room further. At this time, the location was moved to the west wing of the sub-basement of the mansion.
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".
With its female appearance destroyed by Beast, "Danger's" consciousness was presumed to still exist within the conflicted consciousness of the Sentinel, but she was shown back in her humanoid form infiltrating S.W.O.R.D.'s headquarters, to ally with Ord of the Breakworld.
With the Danger's conscience gone, the X-Men resorted to using the empty room to train with their students. Later, the student Prodigy built the Danger Cave underneath the X-Mansion, which acted similarly to the Danger Room. 
The final days of the room at the School for Gifted Youngsters was when the rogue X-Man, Bishop, used nanobots to control the Sentinel Squad O*N*E and destroyed it. After the near-death of Professor Xavier, the X-Men relocated to San Francisco and the mansion ruins were left vacant.
Other Danger Rooms
While in Graymalkin Industries, the X-Men utilized Shi'ar technology to create their own Danger Room, but it was abandoned, after the X-Men left Graymalkin Industries. After arriving on Utopia, the X-Men, again, created another Danger Room, with the same intentions of training their youths. Danger had since joined the X-Men and accepted a position as the jailer and rehabilitation director on Utopia.
Jean Grey School for Higher Learning
After Wolverine left Utopia, with many of the X-Men, he returned to the ruins of the Xavier Institute to found a new school, "Jean Grey School for Higher Learning", in honor of one of the first students of Professor Xavier. Headed by Wolverine and Kitty Pryde, this new school shared much of the ideological structure of it's predecessor and, using Shi'ar engineering, Beast incorporated and allowed for Danger Room technology to be utilized in any area of the structure.
The Danger room was a spherical room that could produce holographic images that felt, smelled, sounded, and, most likely, could even taste like real things.
- Viewing Deck: The Danger Room had a circular viewing deck attached to the ceiling, which also held all the controls that powered the room.
- The appointing of the name "Danger Room" was first used by Xavier in Uncanny X-Men 2 after which the narrator describes it as "a huge unfurnished chamber which houses countless hidden perils!"
- On Earth-9047, the equivalent is known as the Dingy Room.
- The Danger Room was shown at the beginning of X-Men: The Last Stand. It was being used to train the students Iceman, Shadowcat, Rogue, and Colossus. Wolverine and Storm were advising the training session. Also it appears like it's Days of Future Past the Danger Room is using to train the students. The thing that is chasing them looks like a Sentinel.
- 399 appearance(s) of Danger Room
- 13 minor appearance(s) of Danger Room
- 70 mention(s) of Danger Room
- 35 image(s) of Danger Room