a Walrus, by David, in 12.4 seconds.
Inspirations for my brain’s conception of this Fastest Possible Walrus included both Jabba the Hutt:

…and beanbag chairs:

Given those inspirations, our Fastest Possible Walrus is, unfortunately, not the ferocious king of the North that walrus aficionados might have hoped for (you have been waiting for our walrus, right?) No, though his tusks are long and sharp, our take on Odobensus rosmarus is a glum fellow, and sedentary. His turn-ons include: arctic beaches and Star Wars films. Turn-offs: brash young Jedis and orcas.