Ian holds Victor to be a terrible fellow! (4)
I believe the answer is:
ivan
'a terrible fellow' is the definition.
(Russian tsar Ivan the Terrible)
'ian holds victor to be' is the wordplay.
'holds' means one lot of letters go next to another.
'victor' becomes 'V' (phonetic alphabet: alpha, bravo, charlie etc.).
'to be' indicates an anagram.
'ian'+'v'='ianv'
'ianv' with letters rearranged gives 'IVAN'.
(Other definitions for ivan that I've seen before include "man who had a terrible reputation" , "Name of six Russian tzars" , "- - the Terrible (Czar)" , "Chap" , "... the Terrible, 16th-century ruler of Russia" .)