This entry contains MAIN PLOT SPOILERS. Here is a list of the Keepers and some of the details of the quests they ask you to perform.
Near the beginning of the game, the main character uncovers the Map Chamber. After going back to get Professor Fig, the two of you meet four living paintings known as The Keepers. It is revealed that they are the ones left behind the clues that started the main character's journey. Each of the Keepers has knowledge about the connection to ancient magic contained within the main character and they ask the user to perform tasks in exchange for these secrets.
Charles Rookwood
Slytherin
Details for this keeper are unavailable at present.
Niamh Fitzgerald
Ravenclaw
Details for this keeper are unavailable at present.
Percival Rackham
Hufflepuff
During the opening moments of the game, the main character sees an ancient memory left behind in a pensieve. That memory is of Percival Rackham and Charles Rookwood setting up the vault at Gringotts. After the main character finds the map room, it is Professor Rackham who is the first to reveal himself.
San Bakar
Slytherin
Details for this keeper are unavailable at present.
There are some additional NPCs who appear in the memories of the Keepers who may be of interest:
Isidora Morganach
Ravenclaw
Curious last name though, right?