One who designs endless list (8)
I believe the answer is:
inventor
'one who designs' is the definition.
'endless list' is the wordplay.
'endless' means to remove the last letter.
'list' becomes 'inventory' (inventory is a kind of list).
'inventory' with its last letter taken off is 'INVENTOR'.
(Other definitions for inventor that I've seen before include "Architect" , "Creator, first to make something" , "Discoverer" , "Innovator, creator" , "Person with idea" .)