"Nag" is the villain in Rudyard Kipling's short story Rikki-Tikki-Tavi simply because the author intended that to be the case and made very clear that this menacing serpent was the villain. A section of Kipling's famed Jungle Book, Rikki-Tikki-Tavi is a fable featuring a brave mongoose protecting its owners and other animals from the huge cobra that lived on the property. The fable's opening poem includes a stanza that leaves no doubt as to Nag's nature:
At the hole where he went in
Red-Eye called to Wrinkle-Skin.
Hear what little Red-Eye saith:
``Nag, come up and dance with death!''
Nag, it will be revealed, is a king cobra, a large, highly-toxic snake that preys on other animals, and will kill any human being that accidentally surprises it during a casual walk in the jungle. To reinforce the point, the mongoose's initial encounter with the cobra occurs immediately following a conversation with birds who describe the loss of one of their chicks to the snake. Responding to the birds' story, and their comment regarding their chick that "Nag ate him," the mongoose expresses curiosity regarding the identity of "Nag." As Kipling describes the scene that follows:
". . .from the thick grass at the foot of the bush there came a low hiss --- a horrid cold sound that made Rikki-tikki jump back two clear feet. Then inch by inch out of the grass rose up the head and spread hood of Nag, the big black cobra, and he was five feet long from tongue to tail. When he had lifted one-third of himself clear of the ground, he stayed balancing to and fro exactly as a dandelion-tuft balances in the wind, and he looked at Rikki-tikki with the wicked snake's eyes that never change their expression, whatever the snake may be thinking of."
The use of the word "wicked" should leave no doubt as to the role Nag plays in this story. Nag, to reiterate, is the villain of the story because the confrontation between mongoose and cobra provides the story's plot and its tension. Lest any reader miss the point, Kipling concludes his story with a second part to the poem that opened Rikki-Tikki-Tavi, in which he describes Nag in rather unflattering terms, noting that the now-deceased cobra was, in life, the "evil that plagued us."