The chap to be leading endlessly astray (6)
I believe the answer is:
daniel
'the chap' is the definition.
'leading endlessly astray' is the wordplay.
'endlessly' means to remove the last letter.
'astray' indicates an anagram.
'leading' with its final letter taken off is 'leadin'.
'leadin' anagrammed gives 'DANIEL'.
'to be' acts as a link.
(Other definitions for daniel that I've seen before include "Book of the Bible; man's name" , "A wise Biblical judge" , "Hebrew prophet rescued from lion's den" , "-- Deronda (Eliot)" , "-- Boone, US frontiersman and folk hero" .)