What was the first vitamin to be discovered and named?

The first vitamin to be discovered was Vitamin A in 1913.

An English biochemist named Frederick Gowland Hopkins found unknown factors present in milk that were not fats, proteins, or carbohydrates, but were required to aid growth in rats.

He called this nutrient “factor A”, and later this fat-soluble nutrient became known as Vitamin A.

Hopkins was later awarded the Nobel Prize in 1929 for his discovery.

Vitamin A is a fat-soluble vitamin that is an essential nutrient. The term "vitamin A" encompasses a group of chemically related organic compounds that includes retinol, retinyl esters, and several provitamin (precursor) carotenoids, most notably β-carotene (beta-carotene). Vitamin A has multiple functions: growth during embryo development, maintaining the immune system, and healthy vision. For aiding vision specifically, it combines with the protein opsin to form rhodopsin, the light-absorbing molecule necessary for both low-light (scotopic vision) and color vision.