Captain Shear is a prehistore finja tiger shark that is the leader of the Seazarein's guardians. He is also the protector of Gray when he goes out on his missions.Normally, He is pressed against Gray's dorsal fin like a barnacle.
An odd fact is that in the last two books of the series, Shear is sometimes called a "great white". What is even weirder is that after he is killed, he is written as being alive again. Quote "I hate to say this, but couldn't you try to talk to Trank again?" asked Shear.
He had just been killed by 500 frills so I dunno how canon that is.