Dorrie is a large, marine dinosaur-like beast in Super Mario 64 who lives in an underground lake in the Hazy Maze Cave. She spends her days swimming in circles but will gladly give someone a ride if they get on her back. It is also possible to steer Dorrie. Just face the desired direction on her head and and she will swim in that direction.
Dorrie returns in the New Super Mario Bros.. Mario can ride on her back to cross large bodies of toxic water in certain levels of World 4. If Mario ground pounds Dorrie, she will move faster through the water.