commentator; explainer
A person who provides commentary or explanation, such as a sports commentator, news analyst, or someone who explains a topic.
He is famous as a TV sports commentator.
The commentator for this book is a renowned scholar.
解説者 focuses on explaining or clarifying facts (often on TV or radio), while 評論家 gives personal judgments and opinions.
Compound of 解説 (explanation, commentary) + 者 (person). The reading is standard on'yomi.