A curator or keeper looks after collections. It may be a private activity, but usually they look after the collections of a cultural heritage institution. Art galleries, museums, libraries or archives have curators. Zoos have zookeepers and underkeepers.
Curators are subject-matter experts who act as managers. It is an official job description in institutions which have collections. The curator's work involves objects of some kind, such as artwork, collectibles, historic items or scientific collections. Curators in zoos are usually called 'keepers', but it is the same idea.
The word curator comes from the Latin word curare, meaning to look after.