One of the most famous of the early RPGs, Bunnies & Burrows had a hard time being taken seriously, but did introduce many ideas now common in RPGs.
[Corrected:] Bunnies & Burrows (B&B) is a role-playing game (RPG) inspired by the novel Watership Down. Published by Fantasy Games Unlimited in 1976, the game centered around intelligent rabbits. It introduced several innovations to role-playing game design, being the first game to allow players to have non-humanoid roles, and the first to have detailed martial arts and skill systems. Fantasy Games Unlimited published a second printing of the game in 1982, and the game was modified and republished by Steve Jackson Games as an official GURPS supplement in 1992.
As rabbits, player characters are faced with dangers mirroring those in the real world. The only true "monsters" in the game are humans, but there are many predators and natural hazards. The characters' position in the food chain promotes an emphasis on role-playing and problem solving over combat."
Source: Wikipedia, "Bunnies_&_Burrows," available under the CC-BY-SA License.