Generate a question that has the following answer: Shankar-da for the following movie plot: A famous star of Bengali films, Arindam Mukherjee (Uttam Kumar), is invited to the capital to receive a prestigious award. All the flights are booked, which forces him to take the train. The morning newspaper arrives and carries with it a detailed article on an altercation he'd been involved in. In the restaurant car, he meets Aditi Sengupta (Sharmila Tagore), a young journalist who edits a modern women's magazine, Adhunika.[2] Filled with contempt for the likes of him, she secretly plans to interview him because she thinks it'd attract more readers. He soon starts to reveal his personality, and also brings to surface the inner insecurities and his consciousness of the limitations of his 'powers'. Aditi initially takes notes, surreptitiously, but later on, out of empathy almost bordering on pity,stops. However, critical of the star, she interrogates him, leading to further introspection on his part. Slowly, his guilt about the way things turned out is very visible. Arindam also mentions Shankar-da, his mentor, who had never wanted Arindam to join films, being a strong opposer of the medium. He talks about his first day in film, and on the different experiences in faced with other workers in the field and some of the things that happened to them. Toward the end of the train journey, Arindam is drunk and feels a need to confide his wrongdoings. He asks the conductor to fetch Aditi. He begins to reveal the reason behind the altercation he was a part of, but Aditi stops him, as she has already guessed. It was an affair he'd had with one of his co-actors, Promila. Afraid that he might commit suicide, Aditi makes sure he returns to his cubicle, before going back to her own. As the star re-lives and examines his life with Aditi, a bond develops between them. Aditi realizes that in spite of his fame and success, Arindam is a lonely man, in need of empathy. Out of respect for him, she chooses to suppress the story and tears up the notes she has written. She lets the hero preserve his public image.
A:
Who was Arindam's mentor?