There are anomalies and special creatures born of every race and species. It is what drives some of them to become adventurers and heroes. But this is not strictly the purview of the heroes – there are monsters and other creatures out there that buck the traditions of their kin and rise to become more. Irrkthul is just one of these creatures.
Irrkthul was always strange, even by goblin standards. He claimed he could hear the stones and rocks talking to him from an early age. The rest of his tribe simply thought he’d been hit in the head by one too many of those stones and rocks and left the young goblin to his own devices. Suffice to say, they were more than a little bit shocked when the goblin was able to display this connection to the caves by manifesting druidic magic! (Of course, they don’t know it’s druidic magic per se, they just know that Irrkthul has some powerful juju.) Because of this fact, he was a shoe in when their chieftain died (finally). Under his leadership, the tribe was able to carve out a vast (for goblins) swath of the underground caverns they called home, absorbing a few smaller tribes in the process. Irrkthul was even able to train several giant bats they found nesting in the caverns below that several of the braver warriors use as mounts to scout various locations (and sometimes even in battle).
Irrkthul is quite a bit more serious and ordered than your standard goblin, a fact that causes both him and the rest of his tribe no small amount of headaches. But in the end, they are able to support each other, and that is what matters. Irrkthul would make a wonderful low-level boss character for the characters to make their name slaying with several adventures to trek through the caves, culminating in a final showdown between the goblin druid and his bat riding warriors in a vast cavern below the earth.