The Oxford English Dictionary defines the Law of the Jungle as "the code of survival in jungle life, now usually with reference to the superiority of brute force or self-interest in the struggle for survival".
[1] The phrase was introduced in Rudyard Kipling's 1894 work The Jungle Book, where it described the behaviour of wolves in a pack.
As the creeper that girdles the tree trunk, the law runneth forward and back; For the strength of the pack is the wolf, and the strength of the wolf is the pack.
The law is maintained by Shere Khan, the jungle's "royal keeper" and protector, who kills anyone who has violated it.
In the 2016 Disney remake of their 1967 animated film The Jungle Book, itself based on the novel, the wolves' poem is described by Baloo as a piece of propaganda.