Qualities defining a great UPSC mentor include experience, patience, and effective communication. An ideal mentor possesses a deep understanding of the examination process and can provide tailored guidance. They should be approachable, allowing aspirants to discuss their difficulties openly. A great mentor encourages critical thinking and instills confidence in candidates, making them feel valued. Additionally, they can motivate aspirants through their insights and personal experiences in overcoming challenges, thereby enhancing the overall learning experience.