The Kzinti (singular Kzin) are a fictional, very warlike and bloodthirsty race of cat-like aliens in Larry Niven's Known Space series.
The Kzinti were initially introduced in Niven's story "The Warriors" (originally in Worlds of If (1966)) and " The Soft Weapon" (1967), both collected in Neutron Star (1968). A Kzin character, Speaker-to-Animals (later known as Chmeee), subsequently played a major role in Niven's Hugo and Nebula award-winning Ringworld (1970) and Ringworld Engineers (1980), giving considerably more background of the Kzinti and their interactions with human civilizations. Following Ringworld, Niven gave permission to several friends to write stories taking place in the time following "The Warriors" but before "The Soft Weapon"; these stories (including a handful by Niven) were collected in a number of volumes of The Man-Kzin Wars, which eventually reached thirteen volumes, the first published in June 1988. Kzinti also appear in Juggler of Worlds (2008) and Fate of Worlds (2012), novels within the Fleet of Worlds series (cowritten with Edward M. Lerner).
The Kzinti were also written by Niven into the Star Trek universe, appearing first in Star Trek: The Animated Series, also in Star Fleet Universe, as well as material for Star Trek: Enterprise that was never aired because of the series being cancelled.