Who was the only person thought to have done all they could do to prevent the full tragedy and loss of life on the Titanic?

The captain of the ship.

Explanation:

The captain of the ship was the only person which have done all they could do to prevent the full tragedy and loss of life on the Titanic because the captain is the leader of the ship and it is his responsibility to save the people on the ship. He order to the crew members to throw the boats in the water before the ship is going inside the water. This action saves many people but large number of people die due to less number of boats.