Given early training by a village hedge-wizard, Mythandir annoyed the old man by his constant questions and incessant failures. He was a curious, if not particularly bright lad, and always wanted to know the reasons why things worked, or what might happen if things were done slightly differently. He took in all the information his master could give him, but that only made him hungry for more so he struck out in search of answers. But not before stealing his master's tomes.
The young tiefling quickly realized that the books were useless to him, many beyond his talents as a fledgling mage. But one stood out from all the others: a volume covered in pebbled leather and locked with a brass seal. Mythandir spent months trying to open the secretive tome to little avail. Then, one night on his own, under the stars, the book seemed to unlock itself. Night after night, Mythandir devoured the contents of this book, learning of Belial, Mephistopheles, Dispater, and the dread lord Asmodeus. Within was a path to power that the new warlock could easily understand: magic wasn't simply a thing to be studied and practiced, it was a gift to be taken and used.
Now Mythandir works to acquire magical knowledge, but he has learned that knowledge is merely the stepping stone to power and it is that which he ultimately desires. In his travels, he discovered a group of adventurers and joined them to further his pursuits. The warlock practically salivates with the idea of long-hidden treasures locked away in some ancient tomb.