normally .you call one .a letterologist.
onithbfdbvb
A catapultist.
I would call him a hobbyist.
A numismatist studies the art and history of coins and coinage. Someone who just collects them is just a collector.
A button collector??
dumb
a hoarder x)
You call someone that studies metal a metallurgist.
A physicist.
Graphologist comes to mind or autograph hunter.
Someone with too much time on their hands and too much space?
a person who studies planets is a planetologist.