Running dog is a literal translation into English of the Chinese pejorative 走狗 (Chinese: zǒu gǒu), meaning lackey or lapdog, an unprincipled person who helps or flatters those more powerful and often evil. It is derived from the tendency of dogs to follow after humans in hopes of receiving food scraps. Historian Yuan-tsung Chen notes that while "In the West, a dog is a man's best friend; but in China, dogs are abject creatures. In Chinese, no idiomatic expression was more demeaning than the term 'running dogs.'"
Historian Chang-tai Hung says the term "imperialist running dog" (diguozhuyi de zougou) was used to invoke negative mental imagery; "The image of...a running dog parallels that of the United States as a wolf. Both bestial representations provide convenient and familiar symbols that political artists can target, but they also validate the use of violence since the annihilation of beasts is justified. ...[The representations of enemies as beasts such as running dogs or rats] call to mind repulsive creatures that inflict damage on the nation."
In 1950 a The China Weekly Review article gave a definition "A running-dog is a lackey, one who aids and accompanies in the hope of being treated kindly and perhaps being allowed to share in the spoils."
In 1953 a The Saturday Evening Post article offered a definition for tso kou ("running dog") and kou t'ui tee ("dog's hips"), saying "A 'running dog' was a person who follows obediently after the person whose dog he is, a fellow traveler; a 'dog's hips' was simply an enthusiastic running dog, who exercises his hips while running errands for his master."
Historian James Reeve Pusey captures some of the power of the idiom when telling of Lu Xun's reaction to seeing people in power mistreat others with the idiom "the weak are the meat of the strong". Lu's anger spilt over to the point of having a reaction even against those calling for resistance without vengeance "For the loudest of such people, he thought, were running dogs of the people-eaters, fed at least on scraps of human flesh."
The phrase running dog has been in use in since the Qing Dynasty, and was often used in the 20th century by communists to refer to client states of the United States and other capitalist powers. Its first recorded use in English was in Edgar Snow's 1937 reportage Red Star Over China:
“Vanguards of young Moslems were . . . urging the overthrow of the ‘Kuomintang running-dog’”.