The Known Space short story by Larry Niven which introduced the Kzin, a cat-like race of aliens to his readers. The Kzin were the first extraterrestrial race encountered by humans, and unexpectedly, from the now peace loving humans standpoint, were extraordinarily warlike. This story spawned all the Man-Kzin war series, as well as the classic Ringworld. It can be found in a number of books, including the first Man-Kzin Wars collection. Truly a fine piece of sci-fi.