Theodore Dru Alison Cockerell (22 August 1866 – 26 January 1948) was an American entomologist and systematic biologist who published nearly 4,000 papers, some of them only a few lines long.

Cockerell's speciality was the insect order Hymenoptera (bees and wasps), an area of study where he described specimens from the United States, the West Indies, Honduras, the Philippines, Africa, and Asia.

After their marriage in 1900, they frequently went on collecting expeditions together and assembled a large private library of natural history films, which they showed to schoolchildren and public audiences to promote the cause of environmental conservation.

[6] Cockerell was author of more than 2,200 articles in scientific publications, especially on the Hymenoptera, Hemiptera and Mollusca, and on paleontology and various phases of evolution, plus some 1,700 other works, including treatises on social reform and education.

He was one of the most prolific taxonomists in history, publishing descriptions of over 9,000 species and genera of insects alone, some 6,400 of which were bees and some 1,000 mollusks, arachnids, fungi, mammals, fish and plants.

While there, they visited the Royal Botanic Garden Edinburgh where, according to himself in 1937, Isaac Bayley Balfour proved that the plant Primula ellisiae was a distinct species from P. rusbyi.