An iconoclast is “a breaker or destroyer of images, esp. those set up for religious veneration;” or “a person who attacks cherished beliefs, traditional institutions, etc., as being based on error or superstition.” From iconoclastic. Dictionary.com. Dictionary.com Unabridged (v 1.1). Random House, Inc. http://dictionary.reference.com/browse/iconoclastic (accessed: January 23, 2009).
The American Heritage Dictionary says:
The original iconoclasts destroyed countless works of art. Eikonoklastēs, the ancestor of our word, was first formed in Medieval Greek from the elements eikōn, “image, likeness,” and -klastēs, “breaker,” from klān, “to break.” The images referred to by the word are religious images, which were the subject of controversy among Christians of the Byzantine Empire in the 8th and 9th centuries, when iconoclasm was at its height. … It is around this time [the Protestant Reformation] that iconoclast, the descendant of the Greek word, is first recorded in English (1641), with reference to the Byzantine iconoclasts. In the 19th century iconoclast took on the secular sense that it has today…. From iconoclastic. Dictionary.com. The American Heritage® Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. http://dictionary.reference.com/browse/iconoclastic (accessed: January 23, 2009).
There is more information on Dictionary.com’s iconoclast page, of course.