Character Analysis
He's a Cold-Hearted Snake
Kaa has just molted when Baloo and Bagheera find him sunning himself on a rock. He's thirty feet long (yikes), and hates the monkeys because they make fun of him. Teasing Kaa is one of the only things the monkeys can do to him, because Kaa is "everything that the monkeys feared in the Jungle" (3.121). Us, too, monkeys, us, too.
Bagheera uses Kaa's hatred of the monkeys (a.k.a. the Bandar-log) to recruit the snake for Operation Rescue Mowgli when the boy is taken to the monkeys' lair. And it's a good thing, too, since Kaa single-handedly (single-tailedly?) whacks the monkeys good, with a little help from Baloo, and absolutely no help from Bagheera who gets overwhelmed fairly quickly.
At the end of the battle, Kaa hypnotizes them and leads them away, presumably to eat them. This is when Kaa reveals his true reptilian nature: He tells Mowgli that he's considering eating him, too. The man-cub is very similar to a Bandar-log after all. But Mowgli, being much smarter than a monkey, agrees to herd goats Kaa's way whenever he can, and Kaa spares him. Unlike the snakes in "Rikki-tikki-tavi," we see that Kaa does have sort of a softer side, but he's not above caving in to his true nature.
We're not sure what happens to Kaa after the end of the story. Maybe he lives a happy life until getting killed by Jennifer Lopez a hundred years later.