What is the most rare Rolex GMT?

Could you elaborate on the most rare Rolex GMT model, and what sets it apart from other Rolex timepieces? I'm particularly interested in its uniqueness, rarity, and perhaps any special features or stories behind it. Is it a limited edition? What materials were used in its creation? Has it ever been auctioned off, and if so, what was the record-breaking price? Understanding the specifics of this highly coveted timepiece would greatly enhance my appreciation for the Rolex brand and its history of crafting exceptional watches.