Rock is some type of crested penguin. He wears a red bandana at all times, and is almost always seen with a cigarette in official art.
While he has a human form, he seems to prefer his animal form more. His human form wears a grey jacket over a black top, grey slacks, black shoes, and black gloves. A dog tag hangs over his bandana, and his crests are somewhat exaggerated.
Penguin appears to be a cranky, short-tempered sort of person. His hobby is mentioned to be fishing, and he is often seen hanging around Orca; the latter claims they are friends, but Penguin seems to despise him. He dislikes his crests being labeled as eyebrows.
He shows kindness to Squid in the bonus scene he first appears in, most likely tending to his wounds after finding him washed ashore his home and crying. Squid, in more recent Ice Scream works, is seen swimming around Penguin's home island, and the two of them may have become friends.
- Penguin is most likely the friend mentioned by Orca in the bonus scene "Love to Stroll". Orca, upon running into Seguro, tells him that he reminded him of a friend. Though Seguro is a sea serpent and looks far different than Penguin, Orca says they have similar "glares".