Who Captain Guy is
Captain Guy commands the Julia, the Australian whaler that takes the narrator away from the Marquesas. He is unwell and not much of a seaman, leaving him dependent on the officers around him.
His ship has rotten timbers, poor food and too few hands, with several sailors also sick. Guy's illness is part of a wider disorder that makes the crew lose confidence in their command.
Captain Guy and the others in the story
Mr. Jermin, the ship's hard, capable mate, supplies the practical authority that Captain Guy cannot maintain. He knows how to drive the sailors, while Guy relies heavily on his officers.
When the Julia reaches Tahiti, many sailors refuse to sail again under the same captain. The narrator and Doctor Long Ghost stand with them, citing the unsafe ship, Guy's illness and the men's need for rest.
Questions
Who is Captain Guy in Omoo?
Captain Guy is the ailing captain of the Julia, the whaler aboard which the narrator begins his journey.
Who actually runs Captain Guy's ship?
Mr. Jermin, the mate, effectively runs the Julia because Guy cannot command firmly.