On June 12, 1984, Alec J. Jeffreys, a geneticist at the University of Leicester, proposed what is widely recognized as the first modern DNA fingerprinting technique. Jeffreys and his colleagues described a method that used variable patterns in regions of the genome composed of tandemly repeated sequences to generate individual-specific banding patterns when genomic DNA was cut with restriction enzymes and probed with labelled repetitive-sequence probes. These patterns, termed "DNA fingerprints," revealed high levels of polymorphism between unrelated individuals and stable inheritance within families, enabling applications in human identification and kinship analysis. Jeffreys’s discovery built on earlier molecular biology advances: restriction enzyme mapping, Southern blotting (developed by Edwin Southern in the 1970s), and methods to label and detect specific DNA sequences. In his initial work, Jeffreys noticed that multilocus probes targeting hypervariable minisatellite regions produced complex, highly individual banding patterns on autoradiographs. Unlike single-locus methods used later, these multilocus profiles provided a rich, distinctive signal without prior knowledge of specific genetic markers. The immediate implications were profound. Within months, the technique was applied to resolve immigration and paternity disputes and, famously, to assist in a criminal investigation. In 1986, DNA fingerprinting played a central role in both identifying the perpetrator in the Enderby murders in the United Kingdom and exonerating a wrongly accused suspect, demonstrating the method’s forensic potential and ethical stakes. The technique also catalyzed broader scientific and practical developments: the refinement of single-locus profiling, the adoption of short tandem repeat (STR) markers for forensic databases, and the establishment of standardized protocols and statistical methods to evaluate the weight of DNA evidence. As implemented in 1984, DNA fingerprinting had limitations. The multilocus autoradiographic method required relatively large quantities of high-quality DNA, used radioactive probes, and produced complex patterns that often demanded expert interpretation. Over the subsequent decade, technical improvements — non-radioactive probes, polymerase chain reaction (PCR) amplification, and the focus on STR loci — increased sensitivity, reproducibility, and ease of use, allowing forensic laboratories to adopt DNA profiling widely. Jeffreys’s 1984 proposal is documented in the scientific literature and in historical accounts of molecular genetics and forensic science. While later technologies and marker systems supplanted the original multilocus approach in routine forensic practice, the conceptual breakthrough — that inherited variable DNA sequences could serve as a reliable identifier — remains the foundation of modern DNA-based identification. The introduction of DNA fingerprinting also prompted legal, ethical, and social debates: standards for laboratory practice, the statistical interpretation of profile matches, privacy concerns around DNA databanks, and questions about how the technology should be used by law enforcement and immigration authorities. These discussions continue to evolve alongside technological advances. In summary, the proposal of DNA fingerprinting on June 12, 1984, by Alec Jeffreys marked a turning point in genetics and forensic science. It established a new scientific principle and practical tool for individual identification and kinship testing, and set in motion technical, legal, and ethical developments that persist in contemporary genomic practice.