WWF panda logo

The formation of WWF happened at around the same time that Chi-Chi (a giant Panda) was at London Zoo.

According to the history of WWF: "Aware of the need for a strong, recognizable symbol that would overcome all language barriers, the [Founders of WWF] agreed that the big, furry animal with her appealing, black-patched eyes, would make an excellent logo.

Although it is anecdotal, I've also heard that the choice of the panda as a logo was also in part to minimize printing costs (in that it was simply black and white).