Sir John Alexander Hammerton (born 27 February 1871 in Alexandria, Scotland; died 12 May 1949 in London) is described by the Dictionary of National Biography as "the most successful creator of large-scale works of reference that Britain has known".
His first posts in journalism included a period in Nottingham where he first met Arthur Mee, who was to become his lifelong friend. Then, in 1905, he joined Alfred Harmsworth's Amalgamated Press. There he again collaborated with Mee in producing the Harmsworth Self-Educator.
He contributed to the first edition of Mee's Children's Encyclopædia, which appeared in a fortnightly series from 1908 till 1910 before being published in eight large volumes. His contribution consisted of compiling articles on 'Famous Books' and 'Poetry'.
His greatest achievement was Harmsworth's Universal Encyclopædia, which – like the Children's Encyclopædia – was published first as a fortnightly series in 1920–22 and sold twelve million copies throughout the English-speaking world.