noun

a person who is very interested in a particular activity or subject.

a sports car enthusiast

fan,fanatic,devotee,aficionado,addict,lover,admirer,supporter,follower,expert,wizard,connoisseur,authority,pundit,cognoscente,one of the cognoscenti,savant,buff,freak,nut,fiend,maniac,ninja,ham,a great one for,maven,geek,jock,nerd,fundi