John Gray McKendrick FRS FRSE FRCPE LLD was a distinguished Scottish physiologist. He was born and studied in Aberdeen, Scotland, and served as Regius Professor of Physiology at the University of Glasgow from 1876 to 1906. He was co-founder of the Physiological Society.

The Royal Institution Christmas Lectures are a series of lectures on a single topic each, which have been held at the Royal Institution in London each year since 1825. The lectures present scientific subjects to a general audience, including young people, in an informative and entertaining manner. Michael Faraday conceived and initiated the Christmas Lecture series in 1825, at a time when organised education for young people was scarce. Many of the Christmas Lectures were published.