Kline is best known for an apocryphal literary feud with fellow author Edgar Rice Burroughs, in which he supposedly raised the latter's ire by producing close imitations (Planet of Peril (1929) and two sequels) of Burroughs's Martian novels, though set on Venus; Burroughs, the story goes, then retaliated by writing his own Venus novels, whereupon Kline responded with an even more direct intrusion on Burroughs's territory by boldly setting two novels on Mars. Kline's jungle adventure stories, reminiscent of Burroughs's Tarzan tales, have also been cited as evidence of the conflict.[1] While the two authors did write the works in question, the theory that they did so in contention with each other is supported only circumstantially, by the resemblance and publication dates of the works themselves. The feud theory was originally set forth in a fan press article, "The Kline-Burroughs War," by Donald A. Wollheim (Science Fiction News, November, 1936), and afterward given wider circulation by Sam Moskowitz in his book Explorers of the Infinite. Richard A. Lupoff debunked the case in his book Master of Adventure. Among the evidence cited by Lupoff discounting the feud: (1) no comment from either writer acknowledging the feud is documented, and (2) family members of the two authors have no recollection of ever hearing them mention it. In response to Lupoff's investigations Moskowitz identified his original source as Wollheim's article, while Wollheim stated, when questioned on the source of his own information: "I made it up!"

In the mid-1930s Kline largely abandoned writing to concentrate on his career as a literary agent (most famously for fellow Weird Tales author Robert E. Howard, pioneer sword and sorcery writer and creator of Conan the Barbarian). Kline represented Howard from the Spring of 1933 till Howard's death in June 1936, and continued to act as literary agent for Howard's estate thereafter. It has been suggested that Kline may have completed Howard's "planetary romance" Almuric, which he submitted to Weird Tales for posthumous publication in 1939,[2] although this claim is disputed.[3]

Kline's novels normally received serial publication in magazines before their release in book form. The Mars novels appeared in Argosy, and Port of Peril in Weird Tales (as Buccaneers of Venus).

Venus series

1. Planet of Peril (1929)
2. The Prince of Peril (1930)
3. The Port of Peril (1932)

Mars series

1. The Swordsman of Mars (1933)
2. Outlaws of Mars (1933)

Other novels and stories

• "Secret Kingdom," Amazing Stories (November 1929)
• Maza of the Moon (1930)
• "The Man Who Limped," Oriental Stories (October 1930)
• "Spawn of the Comet," Argosy (12 July 1930)
• The Call of the Savage, or Jan of the Jungle (1931)
• "The Thing That Walked in the Rain," Amazing Stories (March 1931)
• "The Dragoman's Secret," Oriental Stories (Spring 1931)
• "The Fang of Amm Jemel," Argosy (9 March 1935)
• "The Murder Room," New Detective (May 1935)
• Jan in India (1935)
• "The Iron World," Thrilling Wonder Stories (August 1938)
• "Stolen Centuries," Thrilling Wonder Stories (June 1939)
• Satans on Saturn, 5-part serial, Argosy (November 1940), with E. Hoffmann Price
• "Meteor Men of Mars," Planet Stories (Winter 1942), with Harry Cord

Weird Tales stories

• "The Thing of a Thousand Shapes" 2-part serial (March/April 1923)
• "The Phantom Wolfhound" (June 1923)
• "The Corpse on the Third Slab" 2-part serial (July/August 1923)
• "The Cup of Blood" (September 1923)
• "The Malignant Entity" 3-part serial (May/July 1924)
• "The Phantom Rider" (November 1924)
• "The Bride of Osiris" 3-part serial (August/October 1927)
• "The Demon of Tlaxpam" (January 1929)
• "The Bird-People" (January 1930)
• "Thirsty Blade" (February 1930), with E. Hoffmann Price
• "Tam, Son of the Tiger" 6-part serial (June/December 1931)
• "Midnight Madness" (April 1932)
• "Lord of the Lamia" 3-part serial (March/May 1935)
• "The Cyclops of Xoatl" (December 1936), with E. Hoffmann Price
• "Spotted Satan" (January 1940), with E. Hoffmann Price
• "Return of the Dead" (July 1943), with Frank Belknap Long

Collections

• The Man Who Limped and Other Stories (1946)