One who collects or gathers together.

"People collect for different reasons. Some succumb to collecting fever with investment in mind; others are taken by the thrill of the search, the reward of the find. Sometimes there seems to be no obvious motive; no clearcut understanding of the urge to collect. How does one explain, for example, someone's innate response to the taste and style of another century? Somehow, it's been said, one object cries out for others to keep it company. You oblige; soon, you're a collector."

Cherished Objects: Living with and Collecting Victoriana. Allison Kyle Leopold. Clarkson N Potter Inc. 1991.

Everybody accumulates something - you could be an accumulator on the verge of becoming a collector, or as someone once said "a traveller poised at the border between curiosity and obsession." Certainly, some collectors can be almost totally absorbed by their obsession with collecting.

"There are two main categories of collector, the classifier and the hoarder. ...the hoarder will yearn for anything that may take his fancy. The classifier...will begin to perceive ever greater beauty in ever duller objects, which aquire an irresistible lustre precisely because they fill a gap. The luckiest collector-classifier is one whose quarry is newly collected (therefore cheap), is historically important and is intrinsically beautiful."

Collecting: The Passionate Pastime. Susanna Johnstone and Tim Beddow. Viking. 1986.

Most of the collectors I talked to fitted into the collector-hoarder category. One admitted about seeing an object that she "just couldn't leave it there, just had to have it - that little porcelain rose, and that cup with a rooster on it. Oh! those things - the jawbone of a kangaroo and a ball of human hair 'string'." Another hoarder admitted that he collected things that people would otherwise throw out.
Collectors derive a fair bit of emotional and intellectual stimulation from their objects: yet another collector mentioned that when he and his wife separated, their collection also got split up; how particularly painful it was losing some of his favourite items. He also advanced a theory as to why humans collect: originally it was to show wealth and attract mates. Eventually the sole purpose of attracting partners became defunct, but people still collected.

Collectors of objects have become ever increasing in recent years. One of the new hobbies is 'collecting', and various companies have taken advantage of this and introduced their own self-limiting 'collectables', such as Beanie Babies, and McD's little toys. It remains to be seen whether such collectables are indeed still collectable in a few decades' time.