Let's say we have a ship with all systems integrated into a electronic network, and we have a human integrated into this electronic network wirelessly through implants to act as a sort of management system. The human can control all functions of the ship mentally just as an extension of the body, and is not physically attached to the ship, so he/she can leave the ship as he/she wants, but will not be able to take control the ship from far way without equipment. Legally, would this make the person the master/captain of the ship, as in he/she has ultimate authority and responsibility over the ship, crew and cargo? What other roles on a seagoing ship could such a person fit?
This depends on who he answers to.
Traditionally in maritime law, the master of the vessel is the captain. This legal distinction is to mark a difference between the actual master, and the current conning officer, pilot, helmsman or such.
If your person has vested in him the power to decide where to go and who to shoot at, he is probably the master of the vessel.
Now if he is not the highest ranking person on board, and especially if he wasn't the only person who could do this, then he would most likely be the conning officer. No helmsman would ever have this level of control of a vessel - helmsman is one of the very first watches new personnel learn, and they couldn't reasonably be expected to maneuver the ship in battle - they just turn the vessel how they were told by the Conn.
If there were commercial shipping lanes with hidden obstructions, this person could also be a pilot. The pilot is brought on board a vessel because he has specific knowledge of where to go and not to go for vessels of a certain draft- accurate to inches. If the system was interoperable, professional pilots could come aboard and take control for the duration of the lane, usually no more than a few miles of difficult waterway.
I think legally it could make this person the captain*, though I guess it wouldn't have to. Captain is mostly a title, and should be the person who knows the big picture of the sea the best, how to make decisions, and how to lead men. If this person just acts as an interface, as in the captain gives an order and this person makes it happen, then it could be a first mate, or maybe some new title. Just being able to run the ship doesn't mean you have to be captain, especially if you aren't familiar with the sea.
That being said, if this person is the captain, and is able to control any part of the ship mentally, do you still need a crew?
* I am not a sea lawyer.
What would this person's status be "legally"? I don't think that question is answerable. As no such technology presently exists, you're asking what the law says about a hypothetical situation that is unlikely to come about any time soon. If and when such a hook-up was invented, who knows what laws governments would pass? Different countries might have different laws.
I suppose we could make guesses based on analogy with current situations. Like -- and I don't claim to be any sort of expert on maritime law -- but the fact that a person is physically in control of a ship doesn't make him the "master" or "captain" of the ship. When the captain gets lunch or goes to sleep and someone else takes over the helm, that person doesn't become the captain. Indeed on navy vessels with large crews, the captain doesn't directly control much of anything. The captain doesn't personally run down to the engine room and set the engine speed, then run to the torpedo room to load and fire a torpedo, etc. He gives orders to others and they carry them out.