The Green Lama first appeared in a short novel entitled The Green Lama in the April 1940 issue of Double Detective magazine. The novel was written by Kendell Foster Crossen using the pseudonym of "Richard Foster". Writing in 1976,Crossen recalled that the character was created because the publishers of Double Detective, the Frank Munsey company, wanted a competitor for The Shadow, which was published by their rivals Street & Smith.

The character, partially inspired by explorer Theos "the White Lama" Bernard, was originally conceived as "The Gray Lama" thinking that he could hide in the shadows and sneak around, but tests of the cover art proved to be less than satisfactory so they changed his color to green. The Green Lama proved to be successful (though not as successful as The Shadow), and Crossen continued to produce Green Lama stories for Double Detective regularly up until March 1943, for a total of 14 stories.

Although appearing in a detective fiction magazine, the Green Lama tales can be considered science fiction or supernatural fantasy in that the Green Lama and other characters are possessed of superhuman powers and super-science weapons. The Green Lama is an alias of Jethro Dumont, a rich resident of New York City. Born July 25, 1903, to millionaire John Pierre Dumont and Janet Lansing. He received his A.B. from Harvard University, M.A. from Oxford, and Ph.D. from the Sorbonne; he also attended Drepung College in Tibet. He inherited his father’s fortune, estimated at ten million dollars, when his father and mother were both killed in an accident while he was still at Harvard. Spent ten years in Tibet studying to be a lama (a Buddhist Spiritual Teacher) and learning many mystical secrets in the process. He returned to America intending to spread the basic doctrines of Tibetan Buddhism (remove ignorance and relieve suffering), but realized that he could accomplish more by fighting crime. He never carried a gun, believing that "this would make me no better than those I fight." Dumont was also endowed with superhuman powers acquired through his scientific knowledge of radioactive salts. He was also noted to wear a rainbow ring of hair. Dumont has two alter egos: the crime-fighting Green Lama, and the Buddhist priest Dr. Pali. He also had additional alter-egos including the adventurer "Hugh Gilmore."

Among the Green Lama's litany of associates were a Tibetan lama named Tsarong, the college educated reformed gangster Gary Brown, the post-debutant Evangl Stewart (who would go on to marry Gary), radiologist Dr. Harrison Valco, New York City police detective John Caraway, actor Ken Clayton, Montana-born actress Jean Farrell, and magician Theodor Harrin. The Green Lama was also frequently assisted by the mysterious woman known as "Magga", whose true identity was never revealed. Crossen's pseudonym "Richard Foster" was also established as a character and friend of Jethro Dumont.