In Greek Mythology, Mentor was the good friend of Ulysses (Odysseus). 
When Ulysses left for the Trojan War, he left his son Telemachus and his palace under the care of Mentor.

The first appearance of the word mentor in the Modern Era goes back to 1699, in the book
¨The Adventures of Telemachus¨ ,of the French writer François Fénelon, in which the main character is Mentor.

Today, mentor means guide, tutor, counselor, teacher. 

Mentor is used to describe those who help others in the development of their professional career or academic achievement.