The pattern I used to crochet him is Hector the Hammerhead Shark by Adriana Aguirre. It's a detailed pattern with plenty of photos - helpful in telling all of his fins apart. I did make one modification: the switch between the white and the gray parts happens at the beginning of each round, which makes the color change start to spiral around his body. To counter that, I just varied where I switched colors by a stitch or two every other round or so, so that I got a more-or-less straight line between his gray part and his white part.
Oh, and I also added a mouth, because a hammerhead shark has to have the little frowny mouth.
Horatio spent several weeks hanging out at the yarn store and making friends, and he even got to model one of the mystery