Richard had three siblings. His older brother Florian died of injuries suffered from abuse by his father. The family lied to the police, saying that he had fallen down a FLIGHT of steps. He had a younger sister, Roberta, and a younger brother, Joseph (1944–2003), who was convicted of raping and murdering a 12-year-old girl. When asked about his brother's crimes, Richard replied: "We come from the same father."

After his murder convictions, Kuklinski took part in a number of interviews during which he claimed to have murdered from over 100 to 250 men between 1948 and 1986, though his recollection of events sometimes varied. Some have expressed skepticism about the extent of Kuklinski's alleged murders, but law enforcement are confident in their belief that he was a serial killer who killed at least several dozen people both at the behest of organized crime bosses and on his own initiative.

Kuklinski claimed that he first killed in adolescence, allegedly using a closet clothes-hanging rod to bludgeon a neighborhood boy who had bullied and teased him. By the mid-1950s, he had earned a reputation as an explosive pool shark who would beat or kill those who annoyed him. Eventually, Kuklinski claimed his Criminal activity brought him to the attention of Newark's DeCavalcante crime family, who hired him for his first gangland slayings.

Beginning in the spring of 1954, Kuklinski began prowling Hell's Kitchen searching for victims. According to author Philip Carlo:

Eventually five unsolved homicides, including the deaths of Hoffman, Smith, Deppner, Masgay, and George Malliband (found in Jersey City on February 5, 1980) were linked to Kuklinski because he had been the last person to see each of them alive.

Kuklinski's first major mistake was discovered on December 27, 1982, when the decomposing body of 37-year-old Gary Smith was discovered under the bed in Room 31 at the York Motel in North Bergen, New Jersey. Smith had been a collaborator of Kuklinski's who often ran car theft scams with him and another man, Daniel Deppner. Kuklinski and Deppner killed Smith on December 23 by feeding him a cyanide-laced hamburger at the York Motel. When Smith took longer to die from the cyanide than Kuklinski expected, he grew impatient and had Deppner strangle Smith with a lamp cord. When Deppner's ex-wife, Barbara, failed to return with a car to remove the body, they placed it in between the mattress and box springs. Over the next four days, a number of patrons rented the room, and although they thought the smell in the room was odd, most of them did not think to look under the bed. According to forensic pathologist Michael Baden, Smith's death would likely have been attributed to something non-homicidal in nature had Kuklinski relied solely on the cyanide; however, the ligature mark around Smith's neck (and, presumably, the fact that the body had been deliberately hidden) proved to investigators that he was murdered.

On September 25, 1983, Kuklinski made another significant mistake when Louis Masgay was found dead near a town park off Clausland Mountain Road in Orangetown, New York, with a bullet hole in his head. Kuklinski, as he had done many times before, attempted to disguise Masgay's time of death by storing his corpse in an industrial freezer for two years. This time, Kuklinski did not allow the body to thaw completely before he dumped it. The Rockland County medical examiner found ice crystals inside the body on a warm September day. Had the body thawed completely before discovery, the medical examiner stated that he probably would have never noticed Kuklinski's trickery. This discovery helped authorities to deduce that Kuklinski used a freezer as part of his modus operandi and led them to give Kuklinski the nickname "Iceman".

Kuklinski earned the nickname "The Iceman" because of his experiments in disguising the time of death of his victims by freezing their corpses in an industrial freezer. Later, he told Carlo that he got the idea from fellow hitman Robert Pronge, nicknamed "Mister Softee", who drove a Mister Softee truck to appear inconspicuous. Pronge taught Kuklinski the different methods of using cyanide to kill his victims. Kuklinski also claimed to have purchased remotely detonated hand grenades from Pronge. Pronge allegedly asked him to carry out a hit on Pronge's own wife and child, which would have been against Kuklinski's stated code against killing women and children. In 1984, Pronge was found fatally shot in his truck.

Starting in 1985, Detective Kane and ATF Special Agent Dominick Polifrone worked with Phil Solimene, a close friend of Kuklinski, to get Polifrone close to Kuklinski. Polifrone posed to Kuklinski as a fellow hitman, Dominic Michael Provenzano. Polifrone told Kuklinski he wanted to hire him for a hit, and recorded Kuklinski speaking in detail about how he would do it. Kuklinski claims in the HBO interview that Solimene was the only friend he did not kill.

On December 17, 1986, it was arranged for Kuklinski to meet Polifrone to get cyanide for a planned murder, which was to be an attempt on a police detective working undercover. After being recorded by Polifrone, Kuklinski went for a walk by himself. He tested Polifrone's (purported) cyanide on a stray dog and saw it was not poison. Suspicious, Kuklinski decided not to go through with the planned murder and went home instead. He was arrested at a roadblock two hours later. A gun was found in the car, and his wife was charged with trying to prevent his arrest.

Prosecutors charged Kuklinski with five murder counts and six weapons violations, as well as attempted murder, robbery, and attempted robbery. Officials said Kuklinski had large sums of money in Swiss bank accounts and a reservation on a FLIGHT to that country. Kuklinski was held on a $2 million bail bond and made to surrender his passport. In March 1988, a jury found Kuklinski guilty of two murders, but found that the deaths were not proven to be by Kuklinski's own conduct, meaning he would not face the death penalty. In all, Kuklinski was convicted of five murders and sentenced to consecutive life sentences, making him ineligible for parole until age 110.

In a 1991 interview, Kuklinski recalled one of the few murders he later regretted committing:

During his incarceration, Kuklinski granted interviews to prosecutors, Psychiatrists, criminologists, the first Writer known was Pavle Stanimirovic and many television producers spoke to him about his Criminal career, upbringing, and personal life. Three documentaries, the last featuring interviews of Kuklinski by forensic Psychiatrist Park Dietz, aired on HBO in 1992, 2001 and 2003. Writers Anthony Bruno, Michael Wells Jr. and Philip Carlo, Pavle Stanimirovic, Burl Barer each wrote a biography of Kuklinski.

In contrast to Carlo's opinion, however, Kuklinski was interviewed by Psychiatrist Park Dietz in 2002 at Trenton State Prison. The two spoke at length, in a videotaped interview, about Kuklinski's upbringing, family life, crimes, and other events in his past. He told the Doctor that he wanted to know what events or mental irregularities made him able to perform the acts of which he was accused. After a lengthy discussion, the Doctor cited nature vs. nurture, stating that his professional opinion was that both played a part in Kuklinski's development into a hitman who could be functional in other aspects of life. The Doctor elaborated that Kuklinski likely inherited antisocial personality disorder from his parents and that the abuse he claims to have suffered from his father reinforced violence, activities requiring a lack of conscience, and a lack of love. Dietz also stated that Kuklinski suffered from paranoid personality disorder, which caused him to kill people for minor slights or criticisms, often long after they occurred.

In 2003, Kuklinski pleaded guilty to the 1980 murder of New York Police Department Detective Peter Calabro. He received another sentence of 30 years. In the Calabro murder, in which Gambino crime family underboss Sammy "The Bull" Gravano was also charged, Kuklinski said he parked his van on the side of a narrow road, forcing other drivers to slow down to pass. He lay in a snowbank until Calabro came by at 2 a.m., then stepped out and shot him with a shotgun. He denied knowing that Calabro was a police officer, but said he more than likely would have murdered him anyway. Kuklinski was kept in Bergen County Jail in NJ in solitary confinement.

In October 2005, after nearly 18 years in prison, Kuklinski was diagnosed with an incurable form of Kawasaki disease, an inflammation of the blood vessels and was transferred to a secure wing at St. Francis Medical Center in Trenton, New Jersey. Although he had asked doctors to make sure they revived him if he developed cardiopulmonary arrest (or risk of heart attack), his then-former wife Barbara had signed a "do not resuscitate" order. A week before his death, the hospital called Barbara to ask if she wished to rescind the instruction, but she declined. Kuklinski died at age 70 on March 5, 2006. His body was cremated.

After Kuklinski paid back the money he owed, he began staging robberies and other assignments for DeMeo and the Gambinos, one of which was making unauthorized copies of pornographic tapes. In 2011, former Gambino associate Greg Bucceroni alleged that Kuklinski often traveled between Philadelphia, New Jersey and New York handling a variety of concerns involving the Gambinos' pornography establishments, including trafficking illegal pornography, debt collection and murder for hire on behalf of DeMeo and Robert "DB" DiBernardo.

Michael Shannon plays Kuklinski in the 2012 film The Iceman based on Anthony Bruno's book The Iceman: The True Story of a Cold-Blooded Killer. The film also stars Winona Ryder as Kuklinski's wife (renamed Deborah), Ray Liotta as Roy DeMeo, Stephen Dorff as Richard's younger brother Joey, and Chris Evans as Robert "Mr. Softee" (renamed "Mr. Freezy") Pronge.

Richard Kuklinski was born in the family apartment on 4th Street in Jersey City, New Jersey, to Stanisław "Stanley" Kuklinski, a Polish immigrant from Karwacz, Masovian Voivodeship and brakeman on the Delaware, Lackawanna and Western Railroad, and Anna McNally from Harsimus, a daughter of Catholic Irish immigrants from Dublin, who worked in a meat-packing plant during Richard's childhood.

Before he became a contract killer, Kuklinski worked in a warehouse in New Jersey. He was married with two sons when he met Barbara Pedrici. She claimed in an interview with The Telegraph's Adam Higginbotham that once, during an argument in a car, during which she told Richard she wanted to see other people, "Kuklinski responded by silently jabbing her from behind with a hunting knife so sharp she didn’t even feel the blade go in. 'I felt the blood running down my back,' she says. He told her that she belonged to him, and that if she tried to leave he would kill her entire family; when Barbara began screaming at him in anger, he throttled her into unconsciousness.