Sleek is a female wild black leopard who is always trying to capture devour and eat the civilized animals who live in Celestville, whom she calls "tame towners".
She resides in the jungle outside Celesteville and she is one of the antagonists of the series. However, in one episode, the kids save her from Prospero who was trying to capture her for profit. As a result, she views Prospero as an enemy and is willing to work with the likes of Dandy Andi & Badou in order to remove his secret camp from her jungle.
Her reasons for attacking and eating other animals appears to be due to her choosing following her natural instincts as a predator and holds disdain towards the "tame towners" to be weak due to choosing to live in civilization. She shares a similar view of other friendly wild animals like Dandy Andi, who she calls "tame mane".
Despite the antagonism towards Andi and the "tame towners" at the end of "Kitty Cornered" she joins them in the savannah Poppernut party after the defeat of Prospero, showing that she is not all bad. In "Flower Power", it is revealed that she lives in some old ruins in the deep jungle where the Stone Sunflower grows. In "Monkey Idol", it is revealed Sleek is a talented singer and Badou convinces her to teach Chiku how to sing in exchange for helping Sleek find a way for her to get some sleep which she hasn't had due to all the Monkey's in Monkeyville practicing for singing contest. In the end, Sleek ends up joining Chiku in singing at the contest which both she and Chiku end up winning.