Character appearing in Voltaire (3)
I believe the answer is:
air
'character' is the definition.
(air can mean a character or mood)
'in voltaire' is the wordplay.
'in' says the answer is hidden in the clue.
'AIR' is hidden in the letters of 'voltaire'.
'appearing' acts as a link.
(Other definitions for air that I've seen before include "- - on a G-string" , "Short song" , "Demeanour" , "If it's hot, it's boastful" , "Skye Boat Song, perhaps" .)