Who is the actual writer of Rudolph Red-Nosed Reindeer?

The actual writer of the story "Rudolph the Red-Nosed Reindeer" is Robert L. May.

He wrote the story in 1939 for Montgomery Ward, a department store chain, as a giveaway for their Christmas promotion.

While the song "Rudolph the Red-Nosed Reindeer" is incredibly famous, it was actually written by Johnny Marks, who also adapted May's story into the popular television special.