His real name is Walter Kovacs, the son of a prostitute who felt he interfered in her business and abused him him viciously. At the age of 10, he was cruelly abused by two bullies who enraged him into attacking them and he was arrested and made a ward of the state when his family life was investigated.
Reaching maturity, he found work as a garment worker and was later facsinated by a new garment with special interior dark liquid masses that continually change into symmetrical patterns like a Rorschach test. When he learned of the murder of Kitty Genovese where a woman was murdered in front of a building full of tenants who didn't bother to help her, he modified the cloth as a mask to become Rorschach to lash out against such criminals.
Eventually, he teamed up with another superhero, Nite Owl (II), in a close association in which Rorschach's natural investigation skills were complimented by his partner's technical skills and resources.
By the 1970's, Rorschach was hunting for a kidnapped girl and found a likely hideout to investigate. To his horror, he realized that the girl was murdered and fed to two German Shepherd dogs. In the face of this atrocity, Kovac's mind snapped and assumed the mental identity of Roschach as a seperate personality. With that change, he killed the dogs and later murdered the kidnapper.
With that, Rorschach terrorized criminals on his own and was an apolocalyptic picketter during the day. He grew even more violent, such as when the practice of freelance masked vigilantes were outlawd, he murdered a notorious rapist and pinned a note on the body saying "Never!" before he dumped it front of a police station.
Spoilers follow
Eventually in the mid 1980s, he investigated a murder and discovered that the victim was The Comedian, a miscreant superhero he admired. Suspecting a plot to eliminate superheroes, he pursued the case based on that theory and interviewed the various informal members of the hero community. Although they do not support his idea, the public pressure motivated exile of Dr. Manhattan and the attempted murder of Adrian Viedt aka Ozymandais seems to support his idea. Eventually, he finds himself framed for the murder of a old retired supervillain and arrested.
Sent to prison, Rorschach find himself the subject to numerous death threats and attacks by vengeful prisoners, but more he more than holds his own. Eventually, he is forcibly freed by Nite Owl and Silk Spectre in order to investigate the series of events happening around them.
Eventually, they learned that the mastermind behind the plot is Adrian Viedt and he and Nite Owl traveled to his home in Antarctica to confront him. However, they were too late to stop him from executing his plan to fake a disasterous visitation of a monsterous alien devastating New York City in order to frighten the world into uniting.
Faced with the fact that exposing this crime could lead to worse world devastation, the other superheroes agreed to keep silent about it. Rorschach, on the other hand, refused on principle to cooperate and was killed by Dr. Manhattan at his own goading.
However, His legacy may have greater consequences. This is because prior to going to Antarctica, he wrote a complete journal about his investigation and sent it to a reactionary fringe newspaper. Whether the journal's contents will be printed and taken seriously by the public is unknown.