Popular time traveller I’d seen as fearless (8)
I believe the answer is:
intrepid
'fearless' is the definition.
('intrepid' can be a synonym of 'fearless')
'popular time traveller i'd' is the wordplay.
'popular' becomes 'in'.
'time' becomes 't'.
'traveller' becomes 'rep' (travel company worker).
'in'+'t'+'rep'+'id'='INTREPID'
'seen as' acts as a link.
(Other definitions for intrepid that I've seen before include "Bold" , "Brave and fearless" , "Invulnerable to fear" , "Fearless, adventurous" , "Fearlessly adventurous" .)