Final answer:
Maurice Wilkins worked most closely with Rosalind Franklin on DNA structure research in his lab, where Franklin's key contributions were made.
Step-by-step explanation:
The person who worked most closely on a day-to-day basis with Rosalind Franklin was Maurice Wilkins. Franklin conducted her groundbreaking work on X-ray diffraction images of DNA in Wilkins' laboratory. This crucial work involved producing high-resolution X-ray diffraction images, such as the famous "Photo 51", which helped reveal the double helix structure of DNA. Despite her significant contributions, Rosalind Franklin was not recognized with the Nobel Prize along with Francis Crick, James Watson, and Maurice Wilkins due to her untimely death before the award was given in 1962.