The quality of a leader that requires them to understand people and maintain good human relations with them is:

Social Skills

Social skills refer to the ability to interact and communicate effectively with others. A leader with strong social skills can understand people's emotions, motivations, and needs, and can navigate relationships and conflicts with empathy and diplomacy. This quality is essential for building trust, fostering collaboration, and creating a positive and productive work environment. It enables a leader to relate to their team members, understand their concerns, and inspire them to perform at their best.