He is a giant rock-like being. Sources say that he and Captain Amelia met while enrolled in Interstellar Academy and he's her best friend. Others say he was hired to be her first mate. Despite his stern appearance, he is quite friendly and outgoing. He has a soft spot for Amelia but their relationship is thought to be professional (though many have reason to believe that there is more!) and he won't tolerate anybody saying something nasty about her. He respects Amelia and looks out for her.
Mr. Arrow first appeared as Dr. Doppler mistook him for the captain, who appeared some time later and complimented the ship conduct. The crew member he was most suspicious of is Scroop, his suspicions were correct as Scroop was very evil and murderous. One night a nearby star went supernova and soon began to form into a black hole. The crew ties themselves to ships to prevent them from being sucked away. Meanwhile, while everyone else is focused on saving their own lives, Scroop sneaks onto the ship's mast and cuts Mr. Arrow's lifeline causing him to fall to his death into the singularity of the black hole. His death is ruled as an accident and no one finds out until Scroop tells the crew after the event, putting the blame on Jim.
There is a slight animation flaw during his role in the film. As you know, he has three fingers on each hand. Yet right when he is reprimanding Jim and Dr. Doppler from saying any "cross-words" about Captain Amelia, you'll notice the hand on Jim's shoulder is showing five fingers but goes back to three when he lets go.