First introduced in the story "Kaa's Hunting" in The Jungle Book, Kaa is a huge and powerful snake, more than 100 years old and still in his prime. In "Kaa's Hunting", Bagheera and Baloo enlist Kaa's help to rescue Mowgli when the man-cub is kidnapped by Bandar-log (monkeys) and taken to an abandoned human city called the Cold Lairs. Kaa breaks down the wall of the building in which Mowgli is imprisoned and uses his serpentine hypnosis to draw the monkeys toward his waiting jaws. Bagheera and Baloo are also hypnotized, but Mowgli is immune because he is human and breaks the spell on his friends.
Kaa is a symbol of cold-blooded power, both physically and psychologically.
Then Kaa came straight, quickly, and anxious to kill. The fighting strength of a python is in the driving blow of his head, backed by all the strength and weight of his body. If you can imagine a lance, or a battering-ram, or a hammer, weighing nearly half a ton driven by a cool, quiet mind living in the handle of it, you can imagine roughly what Kaa was like when he fought... Generations of monkeys had been scared into good behavior by the stories their elders told them of Kaa, the night-thief, who could slip along the branches as quietly as moss grows, and steal away the strongest monkey that ever lived; of old Kaa, who could make himself look so like a dead branch or a rotten stump that the wisest were deceived till the branch caught them, and then—
The python despises poisonous snakes:
Kaa was not a poison snake--in fact he rather despised the poison snakes as cowards--but his strength lay in his hug, and when he had once lapped his huge coils round anybody there was no more to be said.
In The Second Jungle Book, Kaa appears in the first half of the story "The King's Ankus". After Kaa and Mowgli spend some time relaxing, bathing and wrestling, Kaa persuades Mowgli to visit a treasure chamber guarded by an old cobra beneath the same Cold Lairs. The cobra tries to kill Mowgli but its venom has dried up. Mowgli takes a jeweled item away as a souvenir, not realizing the trouble it will cause them, and Kaa departs.
In "Red Dog", Mowgli asks Kaa for help when his wolf pack is threatened by rampaging dholes (the red dogs of the title). Kaa goes into a trance so that he can search his century-long memory for a stratagem to defeat the dogs:
For a long hour Mowgli lay back among the coils, while Kaa, his head motionless on the ground, thought of all that he had seen and known since the day he came from the egg.