Mate

An officer on a ship who sees that the orders of the commander are carried out. If the master is absent or incapable, the next in command.

"So, by and by, I ran away. I said I would never come home again till I was a pilot and could come in glory. But somehow I could not manage it. I went meekly aboard a few of the boats that lay packed together like sardines at the long St. Louis wharf, and humbly inquired for the pilots, but got only a cold shoulder and short words from mates and clerks. I had to make the best of this sort of treatment for the time being, but I had comforting day-dreams of a future when I should be a great and honored pilot, with plenty of money, and could kill some of these mates and clerks and pay for them."

Mark Twain, Life on the Mississippi (1883).