Artist's father a good person one admitted (7)
I believe the answer is:
dadaist
'artist's' is the definition.
(I've seen this before)
'father a good person one admitted' is the wordplay.
'father' becomes 'dada' (dada is a kind of father).
'a good person' becomes 'st' (saint).
'one' becomes 'I' (Roman numeral).
'admitted' means one lot of letters goes inside another.
'dada'+'st'='dadast'
'dadast' enclosing 'i' is 'DADAIST'.
(Other definitions for dadaist that I've seen before include "unconventional painter" , "What Man Ray was" , "Artist favouring irreverence and incongruity" , "Absurdist artist" , "Member of nihilistic art movement of early 20th century" .)