Children's author had a droll disposition (5,4)
I believe the answer is:
roald dahl
'children's author' is the definition.
(children's author Roald Dahl, 1916-1990)
'had a droll disposition' is the wordplay.
'disposition' indicates anagramming the letters.
'had'+'a'+'droll'='hadadroll'
'hadadroll' with letters rearranged gives 'ROALD DAHL'.
(Other definitions for roald dahl that I've seen before include "Children's author" , "author, resident in 21 [BUCKS] - with 13a" , "he wrote" .)