Tom Nook is the shop owner in Animal Crossing, who also sells you your house.
He also makes you work at his store for a short while. He also pays you nothing but bells.
Eventually if you buy more in his shop, he'll make more money.
Which he'll use to build a bigger store.
If you get the biggest one, his two fake-sons will help you on another floor.
Outside of Animal Crossing, he just makes a few cameos.
His Japanese name is たぬきち Tanukichi and he is based on the mythical Japanese Tanuki dog.