How many letters does the top answer for “author of don juan” have?

The most common answer is byron (5 letters).

Crossword clue: author of don juan

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

byron 5 letters wd-fact-v3

English romantic poet notorious for his rebellious and unconventional lifestyle (1788-1824)

author of don carlos 50% similar → schiller

author of don quichotte 50% similar → massenet

author of don quixote 50% similar → cervantes, petipa

wrote don juan 50% similar → byron