From Halopedia, the Halo wiki
Early in their species history, ancient Sangheili came across a world home to ferocious beasts that they came to call the Rafakrit. Eventually there came a point when the rafakrit creatures vanished and they faded away from Sangheili history into myth.
For centuries the Sangheili continued to pass down tales about the rafakrit to new generations. However, over time, their stories devolved into cautionary fables used to teach their young children to listen and take heed. According to these old stories, the rafakrit were said to possess strong aversion to high-pitched noises. As such, when they were out in the dark, Sangheili children were instructed to whistle in order to ward the creatures away.
Growing up, Asum and Dural 'Mdama's mother, Raia, at times retold stories about the rafakrit to them. Although Dural did not care much for the stories, his younger brother was fascinated by them. As a fledgling, Asum would read more about the mythical creatures in archived scrolls that were kept at Bekan keep.
Unknown to the Sangheili, the rafakrit had also been encountered by the ancient Forerunners, who had gathered the animals before the firing of the Halo array and preserved them on their installations, such as Sarcophagus.
Towering the size of a house, the Rafakrit roam around on six thick and muscular legs. They possess a large mouth filled with several rows of daggerlike teeth and have three rows of bright red fins running along their backs. Due to these features, some humans thought of them as looking like "land-sharks". Molly Patel personally thought that the rafakrit's appearance seemed like a frightening combination between the Great red sharks on New Carthage and the Giant crocodiles of Terceira.
List of appearances