A machine/computer created by Professor Charles Xavier
and published in the comics of Marvel Comics
first appeared in Uncanny X-Men #7
In attempting to locate mutants like himself, Charles Xavier created a machine that would locate mutants from the psychic energy emitted from the homo superior brains. The device was called Cerebro after the cerebellum and employed by Xavier in tracking down most of the original X-Men. Cerebro was a convenient plot device to introduce new mutants occasionally or to help locate the X-Men when they were captured or lost. For example, during the late 1970's both Dazzler and Kitty Pryde were first introduced into the Marvel Universe as the result of the tracking power of Cerebro.
In the 1990's in the aftermath of the Onslaught storyline, the X-Men's headquarters fell under the control of a government agency headed by Bastion, whose whole goal was the elimination of mutantkind. Cerebro was taken and Bastion attempted to incoporate the technology into his own to help him track down mutants. Fortunately, Xavier had forseen such an occurance and created a computer virus that would destroy Cerebro should it fall into the wrong hands. What Xavier had not anticipated is that Cerebro would meld with nanite technology of Bastion's systems and achieve sentience.
Cerebro broke free from Bastion's control and set about fulfilling its ultimate goal: the detection and cateloguing of all mutants. Unfortunately, Cerebro took a rather Machievellian approach to its goal and began to use its new found powers to capture mutants. It even employed its nanite technology to appear in the form of Charles Xavier to gain the aid of Kitty Pryde in deactivating the virus that threatened it. To this end, Cerebro also created a group of pseudo-X-Men who were composites of members of the X-Men. Cerebro's X-Men battled the real X-Men as they attempted to take over a sattelite that would help in tracking mutants worldwide. After Cerebro's defeat at the hands of the X-Men, he set about to find his creator Charles Xavier and to use his powers to find all mutants.
Cerebro eventually found Xavier and a mannite named Nina. Xavier used his and Nina's powers to link Cerebro to all humanity. Cerebro was confronted with the differences between all humanity and realized that how it was carrying out its mission was flawed. Cerebro overloaded with information and shut down, "dying" in Xavier's arms.
Xavier has since rebuilt Cerebro and continues to use it in aiding his dream of helping mutants.
Thanks to Ouroboros
for the update on Cerebro