The Golden Dragon starts the game as a "Thief treasure" Boss, meaning that from the very beginning of the game, you’ll have an edge in luring in Thieves.
All the Boss cards in Boss Monster have a treasure type associated with them. Where The Golden Dragon differs is in his unusually powerful Level Up ability. The first time you build out your dungeon to five cards, The Golden Dragon gains one each of all the other treasure types in the game: the Cleric’s Ankh, The Fighter’s Sword, and the Mage’s Tome. That means that suddenly you’ve got a boss who’s contributing to your dungeon’s attractiveness to each and every Hero type. This is huge, and this edge in bidding for Heroes makes other Boss Monsters green with envy. Just be careful... when the Epic Heroes show up in town, you'd better have a powerful dungeon to defeat all the Heroes you'll be luring!
In game lore, The Golden Dragon's dungeon is the most dangerous in the land of Arcadia, and heroes just can’t resist the fame and glory that could come out of adventuring there. He’s the ultimate Boss Monster.