Robert Louis —, writer (9)
I believe the answer is:
stevenson
I believe this clue is a double definition.
'robert louis' is the first definition.
(author Robert Louis Stevenson)
'writer' is the second definition.
(novelist Robert Louis Stevenson)
(Other definitions for stevenson that I've seen before include "Writer of Treasure Island, d. 1894" , "Author of 12 2" , "R L -, Kidnapped author" , "Robert Louis -, Scots novelist" , "Scottish writer" .)