Tux, the Linux Penguin
How did a penguin come to be the mascot for the Linux operating system?
The short answer is that Linus Torvalds, founder of Linux, likes penguins, and he said so when a number of users were discussing what to use as a logo. Larry Ewing created what's now the canonical drawing, and the rest is history.
For a full explanation, see A Complete History of Tux (So Far), by Steve Baker.