Mentors offer guidance to the protagonist and prepare them for the challenges that will face them in the unknown world. Sometimes they will be there constantly to support the hero throughout their journey. Two examples of mentors who provide constant sources of wisdom would be Yoda and Albus Dumbledore.
I will be honest here, I have never seen Star Wars, but I know that Yoda provides counselling and support for Luke Skywalker throughout the series.
Like a good 90s kid, I am a gigantic Harry Potter fan and can talk about Albus Percival Wolfric Brian Dumbledore. Though it turned out that Dumbledore was only using Harry as a weapon against Voldemort, he did make sure that Harry knew how to survive and gain allies up to the point where he would ultimately have to fight the Dark Lord to the death.