James Watson proposed the double-helix structure of DNA with Francis Crick in 1953.
Using chemical data, model building and crucial experimental evidence from other researchers, Watson and Crick published a short structural paper in Nature. Their model placed two DNA strands in opposite directions, with complementary bases paired inside a helical sugar-phosphate framework.
Rosalind Franklin's X-ray diffraction work, especially Photograph 51, provided important evidence about DNA's helical geometry. Maurice Wilkins also contributed experimental data. The 1962 Nobel Prize in Physiology or Medicine went to Watson, Crick and Wilkins; Franklin had died in 1958 and Nobel Prizes are not awarded posthumously.
The double helix explained how DNA could both store information and be copied: each strand can serve as a template for a complementary partner. The historical credit is therefore more collaborative than the simplified version often found in textbooks.