Mallick was born on May 28, 1956, to Zettie Mallick, who was only three months shy of her fourteenth birthday at the time of his birth. Zettie was institutionalized for schizophrenia when she was eighteen. As a result, he was sent to live with his wheelchair-ridden aunt Gertrude, who was a founding member of a bird-watching club in Roanoke, called the Flappers. However, Mallick was socially isolated, with only Gertie to depend on, and he developed an affinity for birds. He also became delusional himself. On March 29, 1973, Gertrude died from natural causes, leaving Mallick alone in their house. Four years later, he snapped and began stalking women around his age, abducting them, dislocating their legs, and leaving them bound in a wheelchair with hopes that the victims would be replacements for Gertie. However, when they couldn't fit his fantasy, he killed them and dumped their bodies in the forests. The deaths caught the attention of then-fledgling FBI agents Gideon and Rossi, who at the time were two of only three agents in the Behavioral Science Unit at the time. When Mallick abducted another woman, Tara Barnett, Tara's mother Mary Ellen pleaded Gideon and Rossi to investigate the case, but in the end, they couldn't launch one due to the short numbers in the unit's ranks, much to Gideon's distress. Meanwhile, Mallick held Tara captive for the next 37 years, his fantasy having been fulfilled by her.
On January 25, 2015, Tara died from cancer, causing Mallick to snap again and go out searching for another woman to abduct and use as a replacement. The discovery of Tara's dumped corpse caught the attention of Gideon, who by that point had resigned from his position following his girlfriend's brutal murder. Having obsessed over the case in the past, Gideon decided to conduct his own independent investigation and deduced that the killer behind the 1978 murders was back. Hoping to lure him out, Gideon ordered some food at a café that was frequented mostly by locals, which he deduced the unsub to be. Coincidentally, Mallick was at the café at the same time. Recognizing him from the newspaper clippings that he kept of his killings, he became threatened by the former agent's presence, tracked him down to a house he owned in the wilderness, and shot him in his dominant hand with a high-powered rifle from outside, in order to weaken him first. Wishing to taunt Gideon before his death, Mallick entered the home, shot Gideon in the stomach, allowed him to see his face, and executed him with a shot to the head. Afterwards, he resumed his search for another replacement for Tara, while the BAU was called over to investigate Gideon's murder.
A few hours after killing Gideon, Mallick lures in his newest target, a woman named Josie Behdart. Pretending to be wheelchair-ridden, he earns her trust after pretending to try to unsuccessfully make a call at a payphone. He then allows her to pet his dog; when she does so, he knocks her out and takes her to the basement of his house, where he dislocates her legs and tries to feed her worms. Eventually, Mallick is identified by the BAU, who go to his house and rescue Josie while he flees, armed with a pistol. Rossi corners Mallick at the backyard of the home, and Mallick puts down his gun. He then tells Rossi that he is willing to go to prison, since his fantasy had been fulfilled after all this time. Rossi, however, puts down his gun as well and tells him that while he may become popular in prison for killing Gideon, a federal agent, he would become a legend if he killed two agents. Mallick agrees and tries to grab his gun, but Rossi is faster and guns him down first, avenging Gideon and Mallick's victims.
From September 1977 to June 1978, Mallick targeted lonely, brunette Caucasian women with little to no self-worth in their early 20s, around the same age he was at the time. He found all of his victims at the local library where his grandmother used to work (except for Tara Barnett, who was found at the supermarket she worked for at the time of her abduction). He would stalk them and lure them to his van with a simple ruse. After subduing them, Mallick would take them over to a basement on his property, where he would dislocate their legs so then they would be reliant on a wheelchair for mobility. He would then kill them by strangling them to death, most likely after they did something to shatter his fantasy, or because he found they couldn't fit his fantasy. His signature was leaving dead Nelson's sparrows clutched in their hands (as a reference to their behavior and lifestyles, since Nelson's sparrows have been figuratively compared with loneliness) after dumping their bodies in the forest. He was initially active every three months, but stopped after abducting Tara Barnett, whom he kept captive since she had fulfilled his fantasy, until her death in 2015.
When he dumped Tara's body, he placed it in a giant homemade nest in the same forest where he dumped his previous victims. Mallick also killed Gideon by shooting him twice to subdue him with a high-powered rifle, then finishing him off with a third shot to the head. He later tried to kill Rossi by shooting him with a pistol.
The unsub who killed Gideon is a white male aged in his late 50s. He shot him from outside Gideon's home while the latter was still inside. This was done out of cowardice and a lack of confidence, which was only regained once he knew he had the upper hand. This kind of mindset suggests the unsub is a hunter. He watched, waited, and hunted him, and also wanted him to know who he was when he killed him, which means the murder was personal. He committed a series of murders in the late 70s but stopped. This could possibly be because he was either forced into hiding after the FBI began investigating his murders, incarcerated for some other crime, or had moved away.
It was later revealed he stopped killing because he found the victim he really wanted, Tara Barnett, and held on to her. However, Tara's recent death caused him to go after another woman. He took the time to bring her body to the forest to dispose of it, but not to bury it, which speaks to his remorse. He abandoned his signature because Tara had become his new obsession. He has a precise comfort zone that has not changed since the original murders. He is a local and a creature of habit, which is how Gideon knew the kinds of places the unsub would go to and why he allowed himself to be noticed: to get his attention. The unsub killed Gideon because he knew he was looking for him and he had to avoid being caught. The age of his victims has stayed the same even though he has gotten older, which indicates an arrested development.
His signature of leaving Nelson's sparrows in the victims' hands seems to be because the birds' behavior matches to that of his victims. He has a high degree of knowledge about birds, so he may be in a bird lovers' club. He knew about Tara because he was watching her longer than his previous victims. Neither he nor Tara were very social, so he would have had to find her somewhere connected to her, such as the supermarket she worked at prior to her abduction. He may have even worked there to be close to her and most likely still works there now.
- September: Unnamed woman
- December: Unnamed woman
- March: Unnamed woman
- June: Tara Barnett (abducted, dislocated her legs repeatedly, and held captive for 37 years; died in 2015 of cancer that went untreated during her captivity)
- Mallick currently has the longest cooling-off period of any other serial killer featured in Criminal Minds to date, being inactive for 37 years between his abduction of Tara Barnett and his murder of Gideon.
- Season Ten
- Season Eleven
- Season Twelve
- "Hell's Kitchen" (mentioned)