Powerful wraiths sometimes choose to aid Enfants, molding them into allies for the future. These lieges, or Mentors, have their own personal reasons for aiding the young and weak. Some want reliable underlings; others try to fulfill their Passions through altruism.
The Mentor Background can also reduce the experience point cost when learning new Arcanos. If a character wants to learn a new Arcanos possessed by her Mentor, the player may roll a number of dice equal to the number of dots in Mentor; each success subtracts one from the number of experience points needed to learn the Arcanos.
Mentor has little power but is occasionally helpful.
Mentor has some degree of status; her advice is sparse, but useful.
Your Mentor knows a great deal and shares much of this with you.
A wise old Gaunt has chosen to pass on his knowledge to you.
If your Mentor doesn't know it, then few if any among the Restless do.