curator

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One who manages or oversees, as the administrative director of a museum collection or a library.

from The Century Dictionary.

• noun In Scotch law, one appointed as guardian for minors, incompetents, etc.
• noun In Roman law, one appointed to manage the affairs of a person past the age of puberty when from any cause he has become unfit to manage them himself.
• noun In civil law, a guardian; specifically, one who has the care of the estate of a minor or other incompetent person.
• noun One who has the care and superintendence of something, as of a public museum, fine-art collection, or the like.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who has the care and superintendence of anything, as of a museum; a custodian; a keeper.
• noun One appointed to act as guardian of the estate of a person not legally competent to manage it, or of an absentee; a trustee; a guardian.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A person who manages, administers or organizes a collection, either independently or employed by a museum, library, archive or zoo.
• noun One appointed to act as guardian of the estate of a person not legally competent to manage it, or of an absentee; a trustee.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the custodian of a collection (as a museum or library)