Captain Robert FitzRoy was a rising officer in the Royal Navy when he was appointed by the Admiralty to conduct a survey of the coast of South America in HMS Beagle. He wanted a naturalist to accompany the voyage, and also somebody who would function as a gentleman's companion for himself. Darwin's professor at Cambridge, John Stevens Henslow, recommended him for the post. Darwin and FitzRoy shared a small cabin at sea for five years. Darwin's nickname aboard ship was "Philosopher." FitzRoy was noted for his qualities as a naval officer and commander, but also for his temper. When coming on watch, the relieving officers were accustomed to ask "If much hot coffee had been served?"

    FitzRoy was an advocate of the civilizing effects of slavery. In one incident, he described to Darwin how the owner of a great plantation had called his slaves around him, and asked if they wished to be free: they replied No. Darwin demanded of FitzRoy ("perhaps with a sneer") if the Captain thought the word of a slave in the presence of his master was worth anything. Affronted, FitzRoy ordered Darwin to leave his cabin, but shortly thereafter invited him back.