How many letters does the top answer for “a person who is in charge” have?

The most common answer is chief (5 letters).

Crossword clue: a person who is in charge

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

chief 5 letters wn-def

a person who is in charge

a person in charge of paying wages 50% similar → paymaster

the person in charge of a post office 50% similar → postmaster

the person in charge of a railway station 50% similar → stationmaster