Pompous fool like Tiberius, ultimately (3)
I believe the answer is:
ass
'pompous fool' is the definition.
(I've seen this before)
'like tiberius ultimately' is the wordplay.
'like' becomes 'as'.
'ultimately' suggests the final letters.
The last letter of 'tiberius' is 's'.
'as'+'s'='ASS'
(Other definitions for ass that I've seen before include "Clinton's behind" , "Dipstick" , "Long-eared animal" , "Animal of horse family" , "Horse relative" .)