He's known for his ferocity and skill in fanciful art (6)
I believe the answer is:
tartar
'he's known for his ferocity' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'skill in fanciful art' is the wordplay.
'skill' becomes 'art' (both can mean a talent).
'in' is an insertion indicator.
'fanciful' indicates an anagram (a fanciful or silly ordering of the letters).
'art' is an anagram of 'tar'.
'art' going within 'tar' is 'TARTAR'.
'and' is the link.
Can you help me to learn more?
(Other definitions for tartar that I've seen before include "Sauce often accompanying fish" , "Fearsome person: kind of sauce" , "This sauce often goes with fish" , "Dental deposit" , "A ferocious person" .)