John Caius MD (born John Kays) 6 October 1510 – 29 July 1573, also known as Johannes Caius and Ioannes Caius, was an English physician, and second founder of the present Gonville and Caius College, Cambridge.
Caius was born in Norwich and was educated at Norwich School. In 1529 he was admitted as a student at what was then Gonville Hall, Cambridge, founded by Edmund Gonville in 1348 - where he seems to have mainly studied divinity.
After graduating in 1533, he visited Italy, where he studied under the celebrated Montanus and Vesalius at Padua. In 1541 he took his degree as a physician at the University of Padua.
In 1543 he visited several parts of Italy, Germany and France and then returned to England. Upon his return from Italy he Latinised his surname, an action which although self-aggrandising, was somewhat fashionable at the time.
Caius was a physician in London in 1547, and was admitted as a fellow of the College of Physicians, of which he was for many years president.
In 1557 Caius, at that time physician to Queen Mary, enlarged the foundation of his old college, changed the name from "Gonville Hall" to "Gonville and Caius College," and endowed it with several considerable estates, adding an entire new court at the expense of £1,834. He accepted the mastership of the college 24 January 1559 on the death of Dr Bacon, and held it until about a month before his own death.
He was physician to Edward VI, Queen Mary and Queen Elizabeth. From this position he was dismissed in 1568 on account of his adherence to the Roman Catholic faith. He was incongruously accused both of atheism, and of keeping secretly a collection of ornaments and vestments for Roman Catholic use. The latter were found and burned in the College court.
He was elected nine times president of the College of Physicians, an account of which, Annales collegii medicorum 1520-1565, he left in manuscript.
He returned to Cambridge from London for a few days in June 1573, about a month before his death, and resigned the mastership to Thomas Legge, a tutor at Jesus College. He died at his London house, in St Bartholomew's Hospital, on 29 July 1573, but his body was brought to Cambridge, and buried in the chapel under the monument which he had designed.
The question of whether John Caius was the inspiration for the character of Dr Caius in Shakespeare's play the Merry Wives of Windsor has been discussed at length by Arnold McNair, 1st Baron McNair.
Caius was a learned, active and benevolent man. In 1557 he erected a monument in St Paul's Cathedral to the memory of Thomas Linacre. In 1564, he obtained a grant for Gonville and Caius College to take the bodies of two malefactors annually for dissection; he was thus an important pioneer in advancing the science of anatomy. He probably devised, and certainly presented, the silver caduceus now in the possession of Caius College as part of its insignia. He first gave it to the College of Physicians, and afterwards presented the London College with another.
Caius was also a pioneer naturalist, prepared to make his own observations about nature rather than simply relying on accepted authorities. He was ready to make journeys about the country to see and record unusual animals. As such he could be considered also a pioneer of Zoology, not yet recognised as a separate science.
He corresponded with the Swiss naturalist Conrad Gesner, with whom he had made friends while returning from Padua. He wrote a study of British dogs to send to Gesner as a contribution (not used) to his Historiae animalium, and also sent him drawings of dogs, which were printed in later editions of Gesner's work. Caius' Catholic religious convictions did not prevent his friendship with the Protestant Gesner (indeed, the Historiae Animalium, to which Caius contributed, was under Pope Paul IV placed on the Roman Catholic Church's list of prohibited books).
His last literary production was the History of Cambridge University, Historia Cantabrigiensis Academiae (London, 1574).