The use of ‘protagonist’ in place of ‘proponent’ has become common in the 20th century and may have been influenced by a misconception that the first syllable of the word represents the prefix pro- (ie. ‘favoring’) rather than proto-, meaning first (as opposed to deuter-, second, in deuteragonist, or tri-, third, in tritagonist). For example, usage such as “He was an early protagonist of nuclear power” can be replaced by ‘advocate’ or ‘proponent’.
So, now that you know that, go read this post about language protagonist. Great read.
