Gulliver is the pet of Anemone. It is immensely overweight, and therefore can not be easily transported or moved.
Later on in the series, Dominic Sorel takes the job of looking after Gulliver after finding him stowed away in his briefcase. The animal immediately takes a liking to Dominic's bed and could not be moved from its place. It seems to enjoy eating jam. He takes a liking to Dominic over time, and wishes to come with him to stop Anemone from destroying the Scub Coral Control Cluster. After theEND's Vascud Crisis knocks Dominic off his ref board, Anemone jumps out of theEND to go after Dominic, and Gulliver pulls them together.
Gulliver is proposed to be some kind of badger, but nobody really knows for sure as there has never been an official Gulliver phylogeny reveal.
Gulliver is a reference to Anemone's namesake's pet alligator in the book Coin Locker Babies. I flipping love Gulliver