The word dominant comes from the 15th-century Middle French word dominant, which derives from the Latin dominari (to rule or govern).  This Latin verb ultimately stems from dominus, meaning "lord," "master," or "head of a household".  

According to the Oxford English Dictionary (OED), the adjective dominant was first used in English in the mid-1500s.  The earliest known recorded use of the word dates to around 1533 in the writings of Giles Du Wes, a musician and royal tutor who taught French to English nobility.  The original meaning was rooted in exerting chief authority or command. Over time, the word branched out into several specific fields.  General/Biology: Jean-Baptiste Lamarck and later Charles Darwin used it in the 19th century to describe species or languages that spread and supersede others. It was popularized in genetics by Gregor Mendel to describe the trait that masks a recessive one.  Music Theory: Although Rameau codified the musical concept (the fifth note of a scale) in the 18th century, English musicologists adopted the term later to describe a note or chord that "dominates" and has a strong pull back to the tonic. 

Related words:  Dominate (verb): First recorded in 1611.  Dominance (noun): First recorded in 1823.  Autosomal dominant (genetics): First recorded in 1919. 

Dominant characters—whether protagonists, antagonists, or force-of-nature figures— drive the narrative forward. They dictate the plot, force conflict, and anchor the reader's emotional connection, transforming passive events into a dynamic, compelling journey.