What type of source are biographies considered when discussing influential leaders?

Biographies are classified as secondary sources when discussing influential leaders. This classification originates from the nature of biographies, as they provide interpretations and narratives of a leader's life based on the review of primary sources, such as letters, speeches, and other firsthand accounts. These secondary sources are valuable for offering context, analysis, and insight into the person's impact and legacy, but they do not present original content and experiences directly from the subject themselves.

When analyzing the other options, primary sources refer to original documents or firsthand accounts related to the subject. Credibility is an attribute of a source but does not define the type. Tertiary sources typically compile and summarize information from secondary and primary sources, such as encyclopedias or databases, but biographies offer a deeper narrative that usually pulls from various resources rather than just summarizing information. This differentiation highlights that biographies serve as interpretations rather than direct evidence or foundational facts.