Collectors are Beasts who hunger for a hoard. The items they hoard may not be intrinsically valuable, and may not even be physical objects (one example character hoards secrets). By stealing or otherwise seizing these items, Collectors teach humans that nothing lasts forever.
Generally Collectors maintain one or more hoards in a highly secure location. Some meticulously organize and catalogue their hoards; others value the acquisition of the object over the possession of it, and just simply toss each new item into a pile.
At high levels of Satiety, the Collector can only be satisfied by adding to their hoard something that meets a long list of exacting criteria. As Satiety falls, they become less particular, until anything in the right general category will do. The actual fear they feed on comes in the moment the previous owner realizes the item in question is gone.