A person who hoards things that you have would be called..."you." Or whatever your name is.
bookworm
A miser. It's pronounced "my zer".
miser
a miser
The definition of a miser is a greedy person who hoards all his money. Someonewho lives very meagerly and never spends money is an example of a miser.
A hoarder
A person who makes of
collecter
A person who looks on the gloomy side of things is pessimistic.
A person who builds things out of stone is called a stonemason or a stoneworker.
a person who discovers new things
You could call them generous or a recipient or a patron.