Final answer:
Joseph Stalin was the leader of the Russian Five who acted as a mentor to others in the circle. He played a significant role as both a political leader and a mentor, transforming the Soviet Union and cultivating a personality cult around his leadership.
Step-by-step explanation:
The leader of the Russian Five and an informal teacher to others in the circle was Joseph Stalin. As a key figure in the Bolshevik Revolution and eventually the leader of the Soviet Union, Stalin was not only a political leader but also a mentor.
He was known for his capabilities as an organizer within the party and for formulating policies that transformed the Soviet Union into an industrial superpower. Stalin's mentorship was influenced by traditional Russian intellectual life where mentorship played a significant role.
During Stalin's tenure, he was surrounded by a cult of personality, where members of his circle highly venerated their leader and Stalin played the dual role of a teacher and father figure to the nation, emphasizing his wisdom and guidance.