After completing her studies in Madrid Margarita Salas moved to New York with her husband Eladio Viñuela to work in Severo Ochoa’s laboratory, clarifying the directionality of ribosome activity in the synthesis of amino acids, a pivotal step in understanding protein biosynthesis. Upon returning to the CSIC in Madrid, Salas initiated a research program on the bacteriophage Φ29. Her most transformative discovery was the Φ29 DNA polymerase, an enzyme with exceptional properties for DNA replication. This enzyme functions as a high-precision, universal DNA copier, enabling faster, more reliable, and more accurate amplification than traditional PCR methods. This Φ29 DNA polymerase revolutionized genetic analysis and is now used worldwide in medicine, forensics, and archaeology. Clinically, it allows early detection of infectious diseases—sometimes even before symptoms appear—and plays a crucial role in oncology, where its high fidelity permits the reliable detection of tumor mutations and its extraordinary sensitivity enables the analysis of circulating tumor DNA without invasive biopsies, facilitating both diagnosis and disease monitoring. Margarita Salas remains an iconic figure in biochemistry, not only for her scientific breakthroughs but also for her leadership and mentorship, inspiring generations of researchers and advancing molecular biology on a global scale.