Hero was first to absorb knowledge (6)
I believe the answer is:
legend
'hero' is the definition.
(I've seen this before)
'was first to absorb knowledge' is the wordplay.
'was first' becomes 'led' (to lead is to go first).
'to absorb' means one lot of letters goes inside another.
'knowledge' becomes 'gen' (I've seen this before).
'led' enclosing 'gen' is 'LEGEND'.
(Other definitions for legend that I've seen before include "Story that may be untrue" , "Traditional story; caption" , "Footnote" , "Caption; very well known" , "Ancient story" .)