What term describes an individual who is considered an expert and has the power to influence others' thoughts and opinions?

The term that best describes an individual who is considered an expert and has the power to influence others' thoughts and opinions is "authority." An authority figure is recognized for their extensive knowledge or expertise in a particular field, which lends them credibility and the ability to sway the perspectives of others. This concept encompasses not just the individual's expertise but also their recognized status among peers or the public, which enables them to guide decisions and influence behavior effectively.

In the context of this question, while expertise relates to the depth of knowledge and skill a person holds, authority specifically captures the aspect of being an expert whose opinions carry weight and can shape the opinions of others. Influence is more general and doesn't necessarily imply expertise; it refers broadly to the ability to affect others' choices or beliefs. Mentorship, while involving guidance and support, specifically implies a relationship characterized by personal development and is not solely about being an expert with influence.

Thus, authority is the most precise term that encapsulates the notion of someone whose expertise allows them to effectively influence others.