He has not appeared nor is he mentioned in any stories so far, but may be in the future.
Cheshwick, true to his name, looks like a humanoid Cheshire Cat; basically the only difference is that you can't see his eyes because his bright yellow hair hangs over his eyes, which are probably a bright amber. His Cheshire Cat smile is nearly perpetual, but he does frown when things go horribly wrong.
Pale, cream colored fur is all over his body, but most of it is hidden behind his red and white sleeveless space suit. He wears no shoes, so instead he walks barefoot, even on molten lava. He can't feel anything in his feet though, because they are perpetually asleep (because of something that went wrong when he was supposedly three years old). His hands are that of a cat's, with sharp black claws, which he unsheaths when not in use. His tail is long and thin, and on the end of his tail is something that looks like a small Cheshire Cat head. (Think Girafarig from Pokemon) The head has a mind of its own, and will usually say opposite to what Cheshwick says.
To make it short, Cheshwick is the exact opposite of Ocarina. He is carefree, and is usually seen lounging about like a house cat on Earth. He is also known as the rule breaker in his Sector (both on his planet and in the GKND), and usually pisses off Ocarina, much to the amusement of others, and up to the point where Ocarina chases him with her Tenta-Hammer.
Cheshwick, however, is also quite knowledgeable on some things, and will usually share information on a subject that is somewhat related to the problem they might face. This also - strangely - upsets Ocarina, and he is subjected to five whacks from her Tenta-Hammer. If that doesn't work, he gets three Roars from Firaga until he begs them to stop, which is rarely.
Sector RIDDLE is Cheshwick's Sector on Planet Cheshurames, and Cheshwick is their Leader / Diversionary Tactics Officer.
He is generally supposed to feel no feelings of attraction to his Sector, partly because he's the only boy in the whole sector, apart from his best friend, Chester. He - unfortunately - has to avoid nearly everyone in his Sector, because they are hopeless fangirls of his.