Which of the following terms signifies a ruler with great authority?

The term "monarch" specifically denotes a sovereign head of state, especially a king, queen, or emperor, who wields significant authority and power over a territory or state. This term is deeply rooted in historical contexts of governance where monarchs often possess absolute or near-absolute control over their domains. The role of a monarch is traditionally associated with legacy, inheritance, and the centralized exercise of power, making it the most fitting option when describing a ruler with great authority.

The other terms present different meanings. For example, "sentinel" refers to a guard or watchman, highlighting a role of observation and protection rather than governance. "Magnate" indicates a wealthy and influential person in business or industry but lacks the connotation of ruling authority inherent in a monarch. "Diversity" pertains to variety and inclusion, which is unrelated to concepts of authority or rulership. Therefore, "monarch" stands out as the term that directly points to a figure of significant ruling power.