John Caius, English physician and academic, co-founded the Gonville and Caius College (died 1573)

John Caius, also known as Johannes Caius and Ioannes Caius, was an English physician, and second founder of Gonville and Caius College, Cambridge. Scholar and physician to Edward VI and Mary I of England.

Gonville and Caius College, commonly known as Caius, is a constituent college of the University of Cambridge in Cambridge, England. Founded in 1348 by Edmund Gonville, it is the fourth-oldest of the University of Cambridge's 31 colleges and one of the wealthiest. In 1557, it was refounded by John Caius, an alumnus and English physician.