As an "evolved feline," Queequeg is capable of human speech and quasi human behavior, although his prerogatives are decidedly feline.
The cat is also a skilled cyyberneticist, who is sometimes called upon when his commander needs assistance with the ship's system. (It is suggested in the books that many of the best cyberneticists are evolved felines).
Unbeknownst to the crew, Queequeg has saved the ship on two occasions He eliminated an infestation of psychic rats intent on spreading the White Plague to the crew. (Book Six: Crucible ). He also fought off a transdimensional alien intruder that only he could see. (Speculative Episode: "I'M IN UR UNDERDECKS. FIGHTIN' UR ALIEN INTRUDERS.")
Queequeg is keeping his own log of the ship's voyage. His log entries serve as the final chapter in Books 1 through 7 and 9.