A historian is a scholar or researcher who uses a wide range of tools, techniques and sources to understand the past and how societies and people have changed over time.
"a" is for when a word starts with a consenant (non-vowel) sound, and "an" is for when a word starts with a vowel sound. We pronounce the H in historian so you would use "a".
Historians are people who trained to investigate the past. Historians show us what the past was like. Some times Historians discover new evidence and consider different interpretations of sources....